U.S. patent number 8,158,689 [Application Number 11/315,576] was granted by the patent office on 2012-04-17 for hybrid absorbent foam and articles containing it.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Andrew T. Baker, Timothy James Blenke, Charles W. Colman, Edward A. Colombo, Jeffrey E. Fish, Michael Joseph Garvey, Jeffrey Jennings Krueger, Mary Frances Mallory, Joseph E. Pierce, Fred Robert Radwanski, Sridhar Ranganathan, Donald E. Waldroup, Kaiyuan Yang.
United States Patent |
8,158,689 |
Baker , et al. |
April 17, 2012 |
Hybrid absorbent foam and articles containing it
Abstract
A hybrid absorbent foam includes an integrated hybrid foam layer
having an open surface, a closed surface, and a foam body extending
between the open and closed surfaces. The integrated hybrid foam
layer has an open-cell content of at least 50%, while the closed
surface provides a barrier to aqueous liquids. The integrated
hybrid foam layer is formed as a single layer, and has a
substantially uniform polymer composition throughout its thickness.
The integrated hybrid foam layer combines the functions of liquid
absorbency, retention, and barrier into a single layer, and is
useful in a wide variety of absorbent articles.
Inventors: |
Baker; Andrew T. (Norcross,
GA), Blenke; Timothy James (Neenah, WI), Colman; Charles
W. (Marietta, GA), Colombo; Edward A. (Penfield, NY),
Fish; Jeffrey E. (Dacula, GA), Yang; Kaiyuan (Cumming,
GA), Garvey; Michael Joseph (Appleton, WI), Krueger;
Jeffrey Jennings (Marietta, GA), Mallory; Mary Frances
(Alpharetta, GA), Pierce; Joseph E. (Appleton, WI),
Radwanski; Fred Robert (Stone Mountain, GA), Ranganathan;
Sridhar (Suwanee, GA), Waldroup; Donald E. (Roswell,
GA) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
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Family
ID: |
37948965 |
Appl.
No.: |
11/315,576 |
Filed: |
December 22, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070148432 A1 |
Jun 28, 2007 |
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Current U.S.
Class: |
521/50;
428/159 |
Current CPC
Class: |
B32B
5/245 (20130101); B32B 5/18 (20130101); B32B
5/32 (20130101); B32B 5/14 (20130101); A61L
15/425 (20130101); B29C 44/5663 (20130101); B32B
5/20 (20130101); B32B 2266/06 (20130101); B32B
2307/7265 (20130101); B32B 2555/02 (20130101); Y10T
428/249953 (20150401); B32B 2307/5825 (20130101); Y10T
428/24504 (20150115); B32B 2266/0228 (20130101); B32B
2432/00 (20130101); B32B 2307/726 (20130101); B32B
2266/0207 (20130101); B29K 2007/00 (20130101); B32B
2266/0292 (20130101); B32B 2266/025 (20130101); B32B
2437/02 (20130101); B32B 2266/0264 (20130101); B32B
2307/54 (20130101) |
Current International
Class: |
C08J
9/00 (20060101); B32B 3/26 (20060101) |
Field of
Search: |
;521/50 ;428/304.4 |
References Cited
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Primary Examiner: Eashoo; Mark
Assistant Examiner: Godenschwager; Peter F
Attorney, Agent or Firm: Armstrong Teasdale LLP
Claims
We claim:
1. A hybrid absorbent thermoplastic foam, comprising an integrated
hybrid thermoplastic foam layer having an edge region, an open
surface, a closed surface and a body having a thickness defined by
a distance between the open and closed surfaces; the open surface
having an open area greater than about 10%; the body having an
open-cell content of about 50% or greater; the closed surface
providing a barrier to the passage of aqueous liquids; the body
having a substantially uniform polymer composition throughout its
thickness; the hybrid absorbent foam having a bending modulus of
less than 6000 KPa at 1 mm deflection, the edge region being
compressed to define a seal about a periphery of the foam.
2. The hybrid absorbent foam of claim 1, wherein the body comprises
an open-celled portion extending inward from the open surface, and
the open-celled portion constitutes at least 50% of the
thickness.
3. The hybrid absorbent foam of claim 2, wherein the open-celled
portion constitutes at least 70% of the thickness.
4. The hybrid absorbent foam of claim 2, wherein the open-celled
portion constitutes at least 90% of the thickness.
5. The hybrid absorbent foam of claim 2, wherein the open-celled
portion constitutes at least 95% of the thickness.
6. The hybrid absorbent foam of claim 1, wherein the body has an
open-cell content of about 60% or greater.
7. The hybrid absorbent foam of claim 1, wherein the body has an
open-cell content of about 70% or greater.
8. The hybrid absorbent foam of claim 1, wherein the body has a
density of about 0.10 grams/cm.sup.3 or less, a saturated capacity
of about 1 gram/gram or greater measured under a load of 3.45 KPa,
and a bending modulus of less than about 6000 KPa at 1 mm
deflection.
9. The hybrid absorbent foam of claim 1, wherein the polymer
composition comprises at least about 45% by weight of a base resin
selected from the group consisting of polystyrene, styrene
copolymers, polyolefins, polyesters, biodegradable polymers, and
combinations thereof.
10. The hybrid absorbent foam of claim 9, wherein the polymer
composition comprises at least about 10% by weight of a
thermoplastic elastomer.
11. The hybrid absorbent foam of claim 10, wherein the
thermoplastic elastomer is selected from the group consisting of
styrenic block copolymers including diblock and triblock copolymers
of styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS),
styrene-isoprene-butadiene-styrene (SIBS),
styrene-ethylene/butylene-styrene (SEBS),
styrene-ethylene/propylene-styrene (SEPS); polyolefin-based
thermoplastic elastomers including random block copolymers
including ethylene a-olefin copolymers; block copolymers including
hydrogenated butadiene-isoprene-butadiene block copolymers;
stereoblock polypropylenes; graft copolymers, including
ethylene-propylene-diene terpolymer (EPDM), ethylene-propylene
random copolymers (EPM) and ethylene propylene rubbers (EPR);
blends of thermoplastic elastomers with dynamic vulcanized
elastomer-thermoplastic blends; thermoplastic polyether ester
elastomers; ionomeric thermoplastic elastomers; polyamide
thermoplastic elastomers; thermoplastic polyurethanes;
biodegradable polymers; and combinations thereof.
12. The hybrid absorbent foam of claim 9, wherein the polymer
composition further comprises a plasticizing agent selected from
the group consisting of polyethylene; ethylene vinyl acetate;
mineral oil, palm oil, waxes, naphthalene oil, paraffin oil, acetyl
tributyl citrate; acetyl triethyl citrate; p-tert-butylphenyl
salicylate; butyl stearate; butylphthalyl butyl glycolate; dibutyl
sebacate; di-(2-ethylhexyl)phthalate; diethyl phthalate; diisobutyl
adipate; diisooctyl phthalate; diphenyl-2-ethylhexyl phosphate;
epoxidized soybean oil; ethylphthalyl ethyl glycolate; glycerol
monooleate; monoisopropyl citrate; mono-, di-, and tristearyl
citrate; triactin (glycerol triacetate); triethyl citrate;
3-(2-xenoyl)-1,2-epoxypropane; and combinations thereof.
13. The hybrid absorbent foam of claim 9, wherein the polymer
composition further comprises a surfactant.
14. The hybrid absorbent foam of claim 1, comprising two of the
integrated hybrid foam layers.
15. The hybrid absorbent foam of claim 14, wherein the integrated
hybrid foam layers are joined at their respective closed
surfaces.
16. The hybrid absorbent foam of claim 1, wherein the open surface
has a surface roughness of about 40 to about 350 microns.
17. The hybrid absorbent foam of claim 1, wherein the compressed
edge region comprises thermal bonds.
18. An absorbent article, comprising at least two integrated hybrid
thermoplastic foam layers, each of the integrated hybrid
thermoplastic foam layers having an edge region, an open surface, a
closed surface, and a body having a thickness defined by a distance
between the open and closed surfaces; the open surface having an
open area greater than about 10%; the body having an open-cell
content of about 50% or greater; the closed surface providing a
barrier to the passage of aqueous liquids; the body having a
substantially uniform polymer composition throughout its thickness;
the integrated hybrid foam layer having a bending modulus of less
than 6000 KPa at 1 mm deflection, the integrated hybrid foam layers
being joined together about at least a portion of their edge
regions with their respective closed surfaces facing each other to
define an open space therebetween.
19. The absorbent article of claim 18, wherein the article
comprises a personal care absorbent article.
20. The absorbent article of claim 18, wherein the article
comprises a medical absorbent article.
21. The absorbent article of claim 18, wherein the article
comprises an industrial absorbent article.
22. The absorbent article of claim 18, wherein the article
comprises a glove or mitt.
23. The absorbent article of claim 18, wherein the open surface and
a portion of the body are apertured and the closed surface is not
apertured.
24. The absorbent article of claim 23, wherein the article is a
wipe.
25. The absorbent article of claim 24, wherein each of the
integrated hybrid thermoplastic foam layers has compressed edge
regions.
26. The absorbent article of claim 18, wherein the article is a
stack of wipes comprising a plurality of wipes superimposed on one
another, and each of the wipes comprises at least one of the
integrated hybrid foam layers.
27. The absorbent article of claim 26, wherein the wipes are
peelably bonded together.
28. The absorbent article of claim 18, comprising a roll of the
integrated hybrid foam layer.
29. The absorbent article of claim 18, wherein at least one of the
integrated hybrid thermoplastic foam layers is pre-saturated with a
deliverable fluid.
30. The absorbent article of claim 29, wherein the deliverable
fluid is a cleaning fluid.
31. The absorbent article of claim 29, wherein the deliverable
fluid is a lotion.
32. The absorbent article of claim 18, wherein the open surface has
a surface roughness of about 40 to about 350 microns.
Description
BACKGROUND OF THE INVENTION
Absorbent, open-celled foams are useful in a variety of absorbent
garments and other absorbent articles for personal care and medical
use. These materials possess dimensional stability, structural
integrity, and an ability to spontaneously recover to an original
shape when squeezed or folded.
In many such applications, a material combination is needed which
receives liquid on one side, and absorbs it, yet which is
substantially leak-proof on the opposing side. To this end,
open-celled absorbent foams have been laminated to another
material, such as a barrier layer, which prevents the expulsion of
liquid on one side. A wide variety of suitable barrier materials
have been developed which are substantially impermeable to water
and aqueous liquids. Some of these materials are breathable to
water vapor, to facilitate wearer comfort of an absorbent garment
containing the material.
Many absorbent garments and other absorbent articles possess
multiple layers which perform different functions. While the
multiple layers optimize the performance of the article, the layers
typically require separate fabrication, processing and cutting, as
well as suitable lamination to each other. In today's cost-cutting
environment, there is a need or desire to simplify the manufacture
of absorbent articles by providing individual materials which
perform multiple functions previously requiring multiple
layers.
SUMMARY OF THE INVENTION
The present invention is directed to a hybrid absorbent
thermoplastic foam and articles containing it. The hybrid absorbent
thermoplastic foam includes an integrated hybrid thermoplastic foam
layer having an open surface, a closed surface, and a body having a
thickness defined by a distance between the open and closed
surfaces. The open surface has an open area of greater than 10%,
suitably higher as explained below. The "open area" is the
percentage of the surface occupied by openings that extend into an
open-cell foam portion of the body, which has an open-cell content
of about 50% or greater. The body (which includes the open and
closed surfaces and the structure between them) has an overall
open-cell content of about 50% or greater. The closed surface
provides a barrier to the passage of liquids. The closed portion of
the body (defining the closed surface) has a thickness which is
small relative to the thickness of the body.
The integrated hybrid foam layer can be extruded as a single layer
and, therefore, has a substantially uniform polymer composition
throughout the thickness of the body. The integrated hybrid foam
layer combines the dual functions of absorbency and liquid barrier
into a single manufactured layer. The integrated hybrid foam layer
may receive aqueous liquid from the open surface, store it in the
body, and retain it in the body due to the liquid barrier function
provided by the closed surface.
The present invention is also directed to personal care absorbent
articles, medical absorbent articles, and industrial absorbent
articles which incorporate the hybrid absorbent foam of the
invention. In particular, the invention is directed to absorbent
gloves, mitts, and wipes.
With the foregoing in mind, it is a feature and advantage of the
invention to provide a hybrid absorbent foam which combines the
functions of liquid intake, storage, and barrier into a single
integrated hybrid foam layer.
It is also a feature and advantage to provide improved, lower cost
absorbent articles which incorporate the hybrid absorbent foam.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an integrated hybrid foam layer.
FIG. 2 is a sectional view of a laminate including two integrated
hybrid foam layers joined at their respective edges with their
closed surfaces facing each other.
FIGS. 3(a)-3(c) are plan views of a mitt and gloves that can be
formed using the laminate of FIG. 2.
FIG. 4 is a sectional view of a wipe that can be formed from the
hybrid absorbent foam, alone or in combination with other
layers.
FIG. 5A is a sectional view of a stack including a plurality of
wipes temporarily joined at their edges.
FIG. 5B is an end view of a rolled product, such as a roll of wipes
or towels, made using the integrated hybrid foam layer of FIG.
1.
FIG. 6 schematically illustrates a tandem extrusion process useful
to make the hybrid absorbent foam.
FIG. 7 illustrates a post-treatment process useful to form the open
surface to make the hybrid absorbent foam.
FIGS. 8A-8B schematically illustrate an apparatus used to perform
the Bending Modulus Test, described herein.
FIG. 9 representatively shows a partially cut away top view of a
saturated capacity tester.
FIG. 10 representatively shows a side view of a saturated capacity
tester.
FIG. 11 representatively shows a rear view of a saturated capacity
tester.
FIGS. 12A-12B representatively show a top view and a side view,
respectively, of the test apparatus employed for the Fluid Intake
Flux Test.
FIG. 13 schematically illustrates an apparatus used to perform the
Vertical Wicking Fluid Flux Test, described herein.
FIGS. 14 and 15 schematically illustrate two areal foam splitting
processes used to make integrated hybrid foam layers of the
invention.
FIGS. 16A and 16B are SEM photographs illustrating the open surface
of a representative hybrid absorbent foam of the invention,
post-treated using cold pin microaperturing.
FIGS. 17A and 17B are SEM photographs illustrating the open surface
of a representative hybrid absorbent foam of the invention,
post-treated using heated pin microaperturing.
FIGS. 18A and 18B are SEM photographs illustrating the open surface
of a representative hybrid absorbent foam, post-treated using
surface texturing. In FIG. 17A, the open surface was prepared by
raising. In FIG. 18B, the open surface was prepared by sueding and
aperturing.
DEFINITIONS
Within the context of this specification, each term or phrase below
will include the following meaning or meanings:
"Cell" refers to a cavity contained in foam. A cell is closed when
the cell membrane surrounding the cavity or enclosed opening is not
perforated and has all membranes intact. Cell connectivity occurs
when at least one wall of the cell membrane surrounding the cavity
has orifices or pores that connect to adjacent cells, such that an
exchange of fluid is possible between adjacent cells.
"Compression" refers to the process or result of pressing by
applying force on an object, thereby increasing the density of the
object.
"Elastomer" refers to material having elastomeric or rubbery
properties. Elastomeric materials, such as thermoplastic
elastomers, are generally capable of recovering their shape after
deformation when the deforming force is removed. Specifically, as
used herein, elastomeric is meant to be that property of any
material which upon application of an elongating force, permits
that material to be stretchable to a stretched length which is at
least about 25 percent greater than its relaxed length, and that
will cause the material to recover at least 40 percent of its
elongation upon release of the stretching elongating force. A
hypothetical example which would satisfy this definition of an
elastomeric material in the X-Y planar dimensions would be a one
(1) inch (2.54 cm) sample of a material which is elongatable to at
least 1.25 inches (3.18 cm) and which, upon being elongated to 1.25
inches (3.18 cm) and released, will recover to a length of not more
than 1.15 inches (2.92 cm). Many elastomeric materials may be
stretched by much more than 25 percent of their relaxed length, and
many of these will recover to substantially their original relaxed
length upon release of the stretching, elongating force. In
addition to a material being elastomeric in the described X-Y
planar dimensions of a structure, including a web or sheet, the
material can be elastomeric in the Z planar dimension.
Specifically, when a structure is applied compression, it displays
elastomeric properties and will essentially recover to its original
position upon relaxation. Compression set is sometimes used to
describe such elastic recovery.
"Open-cell" refers to any cell that has at least one broken or
missing membrane or a hole in a membrane.
"Plasticizing agent" refers to a chemical agent that can be added
to a rigid polymer to add flexibility to rigid polymers.
Plasticizing agents typically lower the glass transition
temperature.
"Polymer" generally includes but is not limited to, homopolymers,
copolymers, including block, graft, random and alternating
copolymers, terpolymers, etc., and blends and modifications
thereof. Furthermore, unless otherwise specifically limited, the
term "polymer" shall include all possible molecular geometrical
configurations of the material. These configurations include, but
are not limited to isotactic, syndiotactic and atactic
symmetries.
"Surfactant" refers to a compound, such as a detergent or wetting
agent, that affects the surface tension of fluids.
"Thermoplastic" is meant to describe a material that softens and/or
flows when exposed to heat and which substantially returns to its
original hardened condition when cooled to room temperature.
"Absorbent article" includes, but is not limited to, personal care
absorbent articles, medical absorbent articles, absorbent wiping
articles, as well as non-personal care absorbent articles including
filters, masks, packaging absorbents, trash bags, mitts, gloves,
stain removers, topical compositions, laundry soil/ink absorbers,
detergent agglomerators, lipophilic fluid separators, cleaning
devices, liquid delivery articles, and the like.
"Personal care absorbent article" includes, but is not limited to,
absorbent articles such as disposable diapers, baby wipes, training
pants, child-care pants, and other disposable garments;
feminine-care products including sanitary napkins, wipes, menstrual
pads, panty liners, panty shields, interlabials, tampons, and
tampon applicators; adult-care products including wipes, pads,
containers, incontinence products, and urinary shields, personal
gloves, mitts, liquid delivery articles, and the like.
"Medical absorbent article" includes a variety of professional and
consumer health-care products including, but not limited to,
products for applying hot or cold therapy, hospital gowns, surgical
drapes, bandages, wound dressings, covers, containers, filters,
disposable garments and bed pads, medical absorbent garments,
gowns, underpads, wipes, medical gloves, mitts, liquid delivery
articles, and the like.
"Absorbent wiping article" or "wipe" includes facial tissue, towels
such as kitchen towels, disposable cutting sheets, away-from-home
towels and wipers, wet-wipes, sponges, washcloths, bath tissue,
gloves, mitts, liquid delivery articles, and the like.
"Industrial absorbent article" includes sponges, cleaning fluid
dispensers, towels, liquid delivery articles, wipes, gloves, mitts,
and the like which are useful in industrial cleaning applications
and, in some instances, household cleaning applications.
"Open-cell foam" refers to a foam having an open-cell content of at
least 50%, measured using ASTM D2856.
"Open area" refers to the percentage of the surface occupied by
openings which extend from the surface at least to an open-cell
portion of the foam body, measured using the Open Area Test
described below.
"Open surface" refers to a foam surface having an open area greater
than 10%, suitably greater than 20%, or greater than 30%, or
greater than 40%, or greater than 50%, up to 80%.
"Closed surface" refers to a liquid barrier surface having no, or
substantially no, open cells or open area. Specifically, a closed
surface should have less than about 5% open area, suitably less
than about 3%, or less than about 1%, or no open area.
"Hybrid foam layer" refers to a foam layer having an open surface,
an opposing closed surface, and an overall open-cell content at
least 50%, measured using ASTM D2856.
"Integrated hybrid foam layer" refers to a hybrid foam layer which
is formed as a single layer, from a single extrusion die, and
therefore has a substantially uniform polymer composition.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a hybrid absorbent thermoplastic foam 10
includes an integrated hybrid thermoplastic foam layer 12 having an
open surface 14, a closed surface 16 and a body 18 having a
thickness "T" defined by the distance between the open and closed
surfaces. The open surface 14 has an open area greater than 10%,
suitably greater than 20%, or greater than 30%, or greater than
40%, or greater than 50%, measured using the Open Area Test
described below. The open area is defined by small openings or
apertures 62 which extend into an open-cell portion 22 of the body
18. Alternatively, the open-cell foam portion 22 may extend to the
surface 14 to provide the open area. The body 18 has an overall
open-cell content of about 50% or greater, or about 60% or greater,
or about 70% or greater or about 80% or greater, measured using
ASTM D2856. The closed surface 16 provides a barrier to the passage
of aqueous liquids, and has an open area content of less than 5%,
or less than 3%, or less than 1%, or zero.
The body 18 includes an open-celled portion 22 extending inward
from the open surface 14 and a closed portion 24 extending inward
from the closed surface 16. The open-celled portion 22 may extend
to the open surface 14, or may begin a short distance inward from
the open surface 14. The open-celled portion 22 and closed portion
24 interface at a boundary 23. The boundary 23 is defined by the
position where all cells immediately adjacent to the boundary 23
are at least 50% open only on one side of the boundary 23, and not
on both sides. The open-celled portion 22 should constitute at
least 50% of the thickness T, suitably at least 70% of the
thickness T, or at least 90% of the thickness T, or at least 95% of
the thickness T. In other words, the closed portion 24 which
defines the closed surface 16 should constitute only a minor
portion of the thickness T of body 18.
FIG. 2 illustrates a hybrid absorbent thermoplastic foam 20, in the
form of a laminate which includes two of the integrated hybrid
thermoplastic foam layers 12. In the embodiment shown, the
integrated hybrid foam layers 12 are bonded together only in edge
regions 26, leaving a pouch or open space 28 defined by the
opposing closed surfaces 16 and the bonded edge regions 26. The
hybrid absorbent foam laminate 20 thus has two outer open surfaces
14 and two inner closed surfaces 16. A less expensive laminate,
useful as a mitt or glove, may include an integrated hybrid foam
layer only on one side and a thermoplastic film or nonwoven web on
the other side.
The hybrid absorbent foam laminate 20 can be used to form a wide
variety of personal care absorbent articles, medical absorbent
articles, and industrial absorbent articles where liquid absorbency
and/or liquid delivery are desired in an outer region or surface
and liquid barrier is desired in an inner region or surface.
Exemplary absorbent articles include without limitation a mitt 30
in FIG. 3(a), including a thumb region 32, a four-finger mitt
region 34 and a cuff 36; the two-finger glove 40 in FIG. 3(b),
including a thumb region 42, two finger-holding regions 44 and 46,
and a cuff region 48; and the four-finger glove 50 shown in FIG.
3(c), including a thumb region 52, four finger-holding regions 53,
54, 55, and 56, and a cuff region 58. The mitt 30 may be used for
delivering a liquid such as a cleaning fluid, lotion, antiseptic,
or the like.
The hybrid absorbent foam laminate 20 is shown in a simple,
relatively inexpensive configuration. Additional layers may be
added to provide increased comfort or structural integrity. For
instance, woven or nonwoven layers (not shown), such as spunbond,
scrim, or meltblown webs, can be provided inward of the closed
surfaces 16 to provide the resulting absorbent article with a soft,
fabric-like feel on the side which contacts the wearer.
The bonded edges 26 of the hybrid absorbent foam laminate 20 may be
formed using any suitable bonding technique. Suitable bonding
techniques include thermal bonding, ultrasonic bonding, adhesive
bonding, stitch-bonding or the like, and combinations thereof. The
optimal bonding technique and conditions will depend on the
particular absorbent article being manufactured, and the bond
strength requirements.
FIG. 4 illustrates an absorbent laminate 60 which can be employed
as a wipe, and/or a cleaning fluid dispenser, and can be tailored
to a variety of personal care, medical, and industrial absorbent
articles and applications. Absorbent laminate 60 includes an
integrated hybrid thermoplastic foam layer 12 in which the
plurality of apertures 62 (or, alternatively, debossments) extend
inward from the open surface 14 and at least partially through the
open-cell portion 22, but do not extend into or through the closed
portion 24 or to the closed surface 16. The apertures 62 are useful
for receiving and distributing a deliverable fluid such as a
disinfectant, cleaning fluid, or the like, in the open-cell portion
22, and for later controlled release and dispensing the deliverable
fluid, typically by squeezing the absorbent article 60. The
absorbent laminate 60 has many fluid delivery properties of a
conventional sponge including cellulosic sponges, and thermoset
(e.g., polyurethane) sponges. The integrated hybrid absorbent foam
layer 12 has densified, compressed end regions 64 which seal and
act as a barrier to the fluid in the absorbent laminate 60 by
preventing lateral spillage. The densified, compressed end regions
64 can be formed using thermal compression bonding techniques.
In effect, the deliverable fluid is contained within the integrated
hybrid foam layer 12 on three sides, bounded by the closed portion
24 and the compressed sealed end regions 64. A plastic or coated
paper liner film (not shown) can be positioned adjacent to the open
surface 14 to further contain the fluid during packaging and
storage of the absorbent laminate 60.
The illustrated absorbent laminate 60 can also include a structural
layer 66 laminated to the closed surface 16. The structural layer
66 can be a nonwoven web (e.g. a film, scrim, spunbond or meltblown
web, or another material), or a much stiffer and stronger material,
depending on the application. If the absorbent laminate 60 is
employed as a personal care wipe or mitt, or medical wipe or mitt,
for instance, the structural layer 66 will likely be contacted with
a user's hand, and should be soft and flexible. If the absorbent
laminate 60 is employed as an industrial wipe, the structural layer
60 should be stiff and strong.
FIG. 5A illustrates a stack 70 of absorbent laminates 72, with each
of the absorbent laminates 72 being similar to absorbent laminate
60 (FIG. 4) except for the absence of an additional structural
layer 66. The absorbent laminates 72 are stacked in pairs, such
that the open surface 14 of each integrated hybrid foam layer 12
faces the open surface 14 of an adjacent integrated hybrid foam
layer 12. This stacking arrangement helps retain the deliverable
fluid within the open-celled portion 22 of each integrated hybrid
foam layer 12 during packaging and storage of the absorbent
laminates 72. Prior to their use as wipes or mitts, the absorbent
laminates 72 may be bonded together at their edges with peelable
bonds 74 and 75, which are easily overcome by pulling the absorbent
laminates 72 apart.
FIG. 5B illustrates a rolled product 80, such as a roll of wipes or
towels, formed of the hybrid absorbent thermoplastic foam 10 of
FIG. 1 wound onto a core 82. The hybrid absorbent foam 10 can be
wound like paper towels and can include tear perforations, but
differs from paper towels in that the hybrid absorbent foam 10 is
resilient so that absorbed liquid can be squeezed out and the foam
10 can be reused. The hybrid absorbent foam 10 also dries quickly,
compared to cellulose absorbents, after being squeezed.
The roll 80 of hybrid absorbent foam 10 can be divided into
individual wipes or towels joined along tearable perforated seams
83 similar to the seams joining paper towels. The wipes or towels
can be used in cleaning and wiping applications such as dishes,
countertops, floors, stovetops, sinks, windows, automobile
exteriors and interiors, and the like. The hybrid foam sheets can
also be used as an absorbent liner for meat cutting boards, or for
drying applications (such as drying an automobile exterior or pet).
The roll 80 of hybrid absorbent foam 10 can also be pre-saturated
with a deliverable fluid for various cleaning applications. The
closed surface 16 faces the user, and is beneficial in protecting
the user from skin contact with the deliverable fluid. In another
embodiment, the absorbent laminate 60 of FIG. 4 can also be
combined with a core 82 and wound into a roll. When the roll 80 is
pre-saturated with a deliverable fluid, it may be desirable to
contain the roll 80 in a closed container to prevent evaporation of
the fluid.
The integrated hybrid thermoplastic foam layer 12 can be produced
from various thermoplastic foaming compositions, including the
compositions described below. Continuous plastic extrusion
processes can initially be utilized to produce an integrated
open-celled foam layer having barrier surfaces on both sides,
followed by post-treatment process(es) tailored to remove or open
up only one of the barrier surfaces, but not the other. Tandem-type
extruders are suitably used for making the integrated foam layer
because of the need for precise control of extrusion temperatures
to produce open-cell foam. The first extruder typically contains
several zones including: feed and conveying, compression, melting,
metering, and mixing zones and if one extruder is being used, a
cooling zone prior to polymer melt discharge, foaming, shaping, and
post-treatment. The first extruder is typically hopper-loaded with
resin and additives using dry/blend/metering equipment and/or
having the additive(s) incorporated into the pelletized polymer
concentrate such as in a masterbatch. The resins, additives, and/or
masterbatch are then heated in the extruder to form a plasticized
or melt polymer system, often with zoned temperature control using
extruder cooling/heating systems. Physical blowing agents are
typically added after the melt temperature has been heated to a
temperature at or above its glass transition temperature or melting
temperature to form a foamable melt. The inlet for a physical
blowing agent is typically between the metering and mixing zones.
The blowing agent can be added at or above saturation levels to
meet desired low density targets. The blowing agent is mixed
thoroughly with the melted polymer at a sufficiently elevated
pressure to prevent melt expansion. With a nucleating agent and
blowing agent blended in the polymer melt, the foamable melt is
typically cooled to a lower temperature to control the desired foam
cell structure. With tandem extruders, the cooling is done in a
second extruder which is connected downstream of the first extruder
through a heated cross-over supply pipe. In single extruders,
including twin screw extruders, cooling is typically done upstream
of the discharge orifice. Often cooling/heating systems with
process temperature control loops are incorporated to tightly
control foam bubble nucleation/growth within the melt. The optimum
cooling temperature is typically at or slightly above the glass
transition temperature or melting point of the melt.
In one embodiment, a tandem extruder, such as illustrated in FIG.
6, can be utilized. This type of extruder arrangement 530 may be
considered particularly suitable in some aspects because it has the
ability to provide precise control of extrusion temperatures to
produce open-cell foam. With tandem extruders 530, the first
extruder section 532 typically contains several zones including a
feed zone 534, a conveying zone 536, a compression zone 538, a
melting zone 540, and a metering and mixing zone 542. The second
extruder section 544 often contains a cooling zone 546 and a
shaping zone 548 prior to the discharge 550. The first extruder 532
is typically hopper-loaded with the base resin(s) as well as any
other desired additives, including thermoplastic elastomers,
plasticizing agents, surfactants and/or fibers, for example.
Techniques known in the art for accomplishing this include using
dry blend/metering equipment and/or having the components
incorporated into a pelletized polymer concentrate such as in a
masterbatch. The components of the foam formula are then heated in
the extruder 532 to form a plasticized or melt polymer.
The foamable melt is then typically cooled to a lower temperature
to control the desired foam cell structure. In the case of tandem
extruders 530, the cooling is typically accomplished in the second
extruder 544 which is connected downstream of the first extruder
532 through a heated cross-over supply pipe 552. In the case of
single extruders (not shown), cooling is typically accomplished
upstream of the discharge orifice. Often cooling/heating systems
with process temperature control loops are incorporated to tightly
control foam bubble nucleation/growth within the gas-laden melt.
The optimum cooling temperature for foam formation is typically at
or slightly above the glass transition temperature or melting point
of the melt.
The melt is then extruded through a die 554 to a lower pressure
(typically atmospheric or a vacuum) and lower temperature
(typically ambient) environment to cause thermodynamic instability
and foaming that cools and crystallizes the polymer composition to
form a stabilized foam 556 that solidifies to form an integrated
foam layer. Circular, annular or slit dies, including curtain dies,
and the like can be used, often with a mandrel, to shape and draw
the foam to the desired gauge, shape, and orientation with foam
expansion and cooling. When the polymer composition is extruded as
a thin foam layer, dual sluice dies can be used to form a suitable
closed surface on one side, having fluid barrier properties.
Various equipment configurations using such extrusion means can be
used to manufacture the foam composite of the present invention. In
addition, various specialized equipment can be employed upstream of
specially designed dies to enhance mixing, cooling, cellular
structure, metering, and foaming. Such equipment includes static
mixers, gear pumps, and various extruder screw designs, for
example. Stretching equipment, including roller nips, tenters, and
belts, may also be used immediately downstream of the discharge to
elongate cellular shape to enhance absorbency, for example.
Microwave irradiation for cross-linking, foaming activation, and
mechanical means can also be used to enhance foam properties. Foam
contouring, shaping (e.g., use of a wire mesh pattern), and the
like, using thermoforming, and other such thermal processes,
including thermal bonding and creping, can be used to control
shaping, flexibility, softness, aesthetics, and absorbent
swelling.
Both physical and chemical blowing agents, including both inorganic
and organic physical blowing agents, are used to create foaming.
Suitable inorganic physical blowing agents include water, nitrogen,
carbon dioxide, air, argon, and helium. Organic blowing agents
include hydrocarbons such as methane, ethane, propane, butanes,
pentanes, hexanes, and the like. Aliphatic alcohols and halogenated
hydrocarbons, including FREON.RTM. and HFC-134A, can also be used
though in the latter, their use is generally avoided for
environmental reasons. Endothermic and exothermic chemical blowing
agents which are typically added at the extruder hopper include:
azodicarbonamide, paratoluene sulfonyl hydrazide,
azodiisobutyro-nitrile, benzene sulfonyl hydrazide, P-toluene
sulfonyl hydrazide, barium azodicarboxylate, sodium bicarbonate,
sodium carbonate, ammonium carbonate, citric acid, toluene sulfonyl
semicarbazide, dinitroso-pentamethylene-tetramine, phenyltetrazole
sodium borohydride, and the like. Mixtures and combinations of
various physical and chemical blowing agents can be used and often
are used to control cell structure. Blowing agent activators can be
added to lower the decomposition temperature/profile of such
chemical blowing agents. Such activators include metals in the form
of salts, oxides, or organometallic complexes.
Open-cell formation can be regulated by elevated processing
pressures and/or temperatures and use of nucleating agents and
chemical blowing agents which can control both cell density and
cell structure. Various base resins are sometimes used to broaden
the foaming temperature to make open-cell foam. Open-cell level can
be facilitated by adding small amounts of various immiscible
polymers to the foam polymer formula such as adding polyethylene or
ethylene/vinyl acetate copolymer to polystyrenic-based foam systems
to create interphase domains that cause cell wall rupture. By
regulating the polymer system components and crystallization
initiating temperature, open-cell content and microporous cell
membrane uniformity can be controlled. Ethylene-styrene
interpolymers can be added to alkenyl aromatic polymers to control
open-cell quality and improve surface quality and processability.
Small amounts of polystyrene-based polymers are sometimes added to
polyolefin-based foams to increase open-cell content. Small amounts
of polyolefins can be added to improve fluid barrier properties of
the closed surface of polystyrene-based foams.
Additives, such as nucleating agents, can also be employed to
obtain desired fine open-cell structure. The amount of nucleating
agent will vary according to the cell structure desired, foaming
temperature, pressure, polymer composition, and type of nucleating
agent utilized. Typically with increasing nucleating agent, cell
density and open-cell content increase. Nucleating agents include
calcium carbonate, blends of citric acid and sodium bicarbonate,
coated citric acid/sodium bicarbonate particles, nanoclays, silica,
barium stearate, diatomaceous earth, titanium dioxide, talc,
pulverized wood, clay, and calcium stearate. Stearic acid,
salicylic acid, fatty acids, and metal oxides can also be used as
foaming aids. Other thermoplastic polymers can also be used for
such purposes. These are typically dry-blended or added with the
polymer concentrate.
Various additives such as lubricants, acid scavengers, stabilizers,
colorants, adhesive promoters, fillers, smart-chemicals, foam
regulators, various UV/infrared radiation stabilizing agents,
antioxidants, flame retardants, smoke suppressants, anti-shrinking
agents, thermal stabilizers, rubbers (including thermosets),
anti-statics, permeability modifiers, and other processing and
extrusion aids including mold release agents, and anti-blocking
agents, and the like can also be added to the foam polymer
formula.
The open-celled foam produced by this process typically has thin
skins defining barrier surfaces on both sides, followed by a
smaller layer of a population of closed cells, followed by
open-celled foam between the barrier skins. In the thermoplastic
extrusion process used to make the foam, the outside surfaces of
the foam form impervious film-like skins. The skin surfaces are
formed with rapid cooling of the outside surfaces upon exiting the
extrusion die and help contain entrapped gas within the polymer
melt long enough for gas diffusion to sufficiently allow foam
expansion and polymer structural solidification. With the rapid
cooling of the polymer melt into a foam structure, an impervious
closed-cell foam structure is typically formed directly beneath the
skin surface. Beneath the closed cellular structure in the middle
portion of the foam laminate is an absorbent open-cell structure.
The outside film skin surfaces and closed-cell structures are dense
and form an "I-beam-like" structure that increases sheet stiffness.
These structures also form a fluid and/or vapor barrier. Fluid and
vapor absorbent products must have access to this middle open-cell
foam structure. To make the integrated hybrid foam layer of the
invention, the skin defining the barrier surface can be removed
from only one side, and not the other. This can be accomplished
using various post-treatment process techniques. For instance, the
barrier surface on only one side may be skinned, sliced off,
needle-punched, brushed, scraped, sanded, buffed, scarved, or
perforated. Following is a detailed discussion of several
post-treatment processes used to remove the barrier surface from
one side of the foam.
A) Pin Microaperturing
To aperture the foam on one side, driven nip rolls wrapped with
Redman flexible wire cloths from Redman Card Clothing Co., Inc. of
Andover, Mass., USA, can be employed. For a foam which is 2-4 mm
thick, the flexible wire cloths may have pins arranged normal to
the nip rolls and the foam sheet and may have diameters of about
0.010-0.18 in (0.254-4.57 mm), pin densities of about 192-312
pins/in.sup.2 (30-48 pins/cm.sup.2), and pin heights of about
1.6-2.4 mm. It has been found that pin density, pin diameter, and
the number of nip treatment passes have quantifiable impacts on
foam fluid intake.
The short pin heights of the flexible wire cloths are useful to
mechanically aperture the foam on one side, thereby effectively
permeating the barrier skin and impermeable closed cells on only
one side. The pins are shorter than the thickness of the foam, so
as to not completely penetrate through the foam sheet to the other
side. Also, the smaller pin diameters referenced above provide
apertures which are small enough so as not to Z-directionally crimp
the foam (given that crimping impairs fluid access). Suitable wire
cloths include Redman PRKC-4 and PRKC-11 having pin heights of 2.4
mm and 1.6 mm, pin densities of 192 pins/in.sup.2 (30
pins/cm.sup.2.) and 192 pins/in.sup.2 (30 pins/cm.sup.2), and pin
diameters of 0.010 in (0.254 mm) and 0.014 in (0.356 mm),
respectively. Seven passes with these microaperturing wire roll
nips were found to provide the foam with enhanced tactile
aesthetics and absorbent functionality including fluid intake and
saturated capacity. The optimal number of passes may vary depending
on the application.
The enhanced flexibility imparted with microaperturing not only
improves absorbency and softness but improves surface texturing
(described in Section C below). Microaperturing increases sheet
flexibility which allows better sheet contact with the moving
surface texturing raising fillets or pins and disrupts the foam
film's outer skin film-like surface to make it less smooth. The
microaperturing also instills a raised surface topography so that
surface texture raising/sueding pins can more readily "grab" and
texture the foam to induce cloth-like and suede rather than
plastic-like visual and tactile aesthetics.
Microaperturing coupled with surface texturing can serve at least
five functions: 1) improved tactile and visual aesthetics, 2)
increased softness and flexibility, 3) enhanced absorbency
properties such as capacity, wicking, and intake, 4) reduced piling
and lint, and 5) minimized loss in sheet strength without
unacceptable basis weight loss. Microapertured foams with
sufficient access to the absorbent open-cells can be used for
personal care, wipes, matts, carrier media, filters, and other
absorbents. In addition, tortuous air flow permeability can be
increased 1000.times. with microaperturing and thereby can allow
the foam to be engineered for construction barrier/thermal and
sound insulation, and controlled fluid release applications.
Use of flexible wire cloths for microaperturing is significantly
less expensive, and yields better properties, than conventionally
fabricated pin aperturing rolls (machined rolls with pressed pins).
Besides the cost advantages, such wire cloths can also readily be
patterned for different X-Y-Z penetration patterns. Because of the
low equipment cost, high hole density treatments can be employed by
utilizing several in-line microaperturing rolls. Because
honeycombed, micro-size, non-through hole aperturing rather than
through-hole or slit aperturing is being utilized, the sheet's
integrity remains high and sheet tear propagation is minimized.
Microaperturing can also be enhanced by heating the pins. With
heated pin microapertured thermoplastic foam, it was seen in
microphotographs that hole size increased from the retraction of
the polymer film that formed the fine thin cellular walls when the
heated pins penetrated into the foam structure. The heated pins
were of sufficient length to penetrate into the internal open-cell
structure. This allowed for a larger effective hole diameter for
better fluid intake without damaging Z-directional open-cell
cavities so fluid was readily absorbed into the foam's internal
structure. By comparing cold (room temperature) vs. heated
(65.degree. C.) pin microaperturing, a smaller heated pin
microaperturing density is needed to obtain improved fluid intake
using the Single Drop Test (below). Initial fluid intake time of
3-5 seconds could be obtained with one heated pin microaperturing
roll nip pass. With cold pin microaperturing, seven roll nip passes
were used to produce a 10 second intake time. Wire cloth
dimensions, roll nip pressures, and number of microaperturing roll
passes were evaluated and found to affect absorbent rates. In
addition, if the foam's surface had previously been surface
textured and then vacuumed to remove excess lint and debris,
reduced Tinting and piling occurred after heated pin
microaperturing. With heat, loosely bound surface protuberances and
piles were more securely thermally bonded to the base foam surface.
Thermally treating the surface textured foam with a heat gun or
oven also reduced linting. Abrasion resistance improved.
To reduce equipment fabrication cost, one microaperturing roll
design option is to use an internally heated microaperturing roll
and a heat-resistant flexible wire cloth. The heated roll would
readily transfer heat to the metal aperturing pins. With the pins
being in contact with the heated roll surface, heat conductance
would readily occur with a heat-resistant silicon-impregnated wire
cloth being less conductive and acting as an insulator. Such
heat-resistant wire cloth can be obtained from Redman Card Clothing
Co., Inc.
FIGS. 16A and 16B are SEM images of the open surface of a
representative integrated hybrid foam layer of the invention,
post-treated using cold pin microaperturing. FIGS. 17A and 17B are
SEM images of the open surface of the representative integrated
hybrid foam layer, post-treated using heated pin microaperturing.
Either technique produces a suitable hybrid absorbent foam.
B) Slitting
Both micro and macro-slitting of the foam can be employed to slit
the foam on one side, thus leaving one of the barrier skins intact.
Using various ultrasonic anvils, different slitting patterns were
evaluated including a preferred "crowfoot" pattern. To slit only
one skin, partially Z-directionally slit apertured arrangements
were produced. With machine adjustment, slits could be produced
that did not crimp the internal hole structure. Various foam basis
weights and densities could be slit. In addition, spunbond could be
bonded to the foam using ultrasonic anvils.
Utilizing fine columnar hydraulic jets (spunlace technology),
micro-slits have been imparted into the foam to enhance absorbency,
softness, and flexibility. This technology has its drawbacks in jet
non-uniformity and web sensitivity to high pressure needling jets
causing excessive micro-slitting that often results in diminished
integrity, and increased tear propagation and rupturing of the
closed barrier surface. There is also the need to dry the foam of
water after hydraulic jet treatment for dry sheet product
applications.
By retrofitting one or more surface texturing raising or sueding
rotating rolls covered with an engineered flexible wire cloth
having longer protruding pins than the base height, pins can be
strategically spaced and located circumferentially around the roll
to micro-slit foam. The rotating roll is speed controlled so that
with a given web speed, the longer protruding pins intermittently
micro-slit a taut-stretched foam sheet by "scratching out" a narrow
furrow within the surface of the foam skin sufficiently deep enough
to penetrate the open-cell absorbent structure. This instills
slitting in the machine direction of the foam and the
micro-slitting depth is adjustable. Such a design can be installed
in surface texture raising/sueding equipment, and the rotating roll
height can be adjusted for controlled foam sheet micro-slitting.
The sheet can be stretched taut across a rotating raising or
sueding drum or moving flat bed and fixed to insure the desired
slitting depth.
C) Surface Texturing
Mechanical brushing (scarfing) of the foam's skin can be employed
to remove one of the barrier skins to diminish the plastic-like
aesthetics and penetrate the closed-cells to allow fluid access to
the open-cell structure. Steel wire brushes can surface texture the
foam but it was determined that more sophisticated brush rolls
would be required to minimize excess removal of material and loss
of web strength. Atlanta Brush, Inc. of Atlanta, Ga., U.S.A. can
supply such trimmed brushes. However, even these brushes can be too
coarse for foam. With this, textile raising and sueding machinery
using fine flexible surface texturing wire cloths having
specifically designed raising or teasing fillets was coupled with
microaperturing. By optimizing machine conditions, acceptable foam
samples were produced having good integrity, absorbency, and
visual/tactile aesthetics. Using Redman raising wires and Saspe's
RapidRaise.RTM./Velura and Durasuede.RTM./VersaTouch textile
machinery, aesthetically appealing surface textured foam can be
produced. This equipment can be obtained from Saspe S.r.l. of
Schio, Italy. The RapidRaise.RTM. process requires relatively
minimum required web tension versus sueding where web tension is
much higher to obtain the necessary working action.
Textile surface texturing equipment has a high processing
efficiency making it a plausible candidate for in-line foam
extrusion. Fine tuning of the machine setup is necessary to obtain
desired properties. Because of the foam's formulation producing a
sheet having high web strength, elasticity, flexibility,
resiliency, and toughness, the sheet is able to withstand the
raising fillets' dynamic and impulsive loadings
The foam skin acts like an "I-Beam." With partial removal of the
skin surface from one or both sides and microaperturing, the
softness and flexibility of the web dramatically improves. With
one-side treatment, fluid barrier properties can be maintained on
the closed surface. If it is desired to surface texture both sides
for tactile aesthetics, optimum control of surface texturing is
needed to avoid penetrating the barrier skin. If desired, the
barrier skin can be made thicker using dual sluice dies and
specially designed single opening dies. With a fibrillated or
suede-like outer-layer surface, visual and tactile aesthetics are
much more cloth-like. By combining raising and/or sueding and
microaperturing, foams have been produced having: Basis Weight
losses typically of <10% Grab MD Tensiles of 10000 grams MD Trap
Tears of >900 grams Grab CD Tensiles of 7000 grams CD Trap Tears
of >350 grams First intake fluid intake flux rates .about.5
ml/sec. Fluid Retention Capacities of >7 g/g Vertical Wicking of
>8.0 cm
By removing .about.10% or more of the basis weight from the surface
of non-microapertured foam, high fluid intake flux intake rates
could be gained; however, the high basis weight loss is not
desirable. Various process and equipment designs include fixing the
web to the rotating raising drum and rolls, fixing the foam to a
rotating drum or moving flat-bed, and rotating the surface
texturing rolls to finely remove or tease the foam skin
surface.
FIG. 18A is a scanning electron microscopy ("SEM") photograph of an
open surface of a representative integrated hybrid foam layer,
post-treated by raising. FIG. 18B is a SEM photograph of an open
surface of a representative integrated hybrid foam layer,
post-treated using a combination of sueding and
micro-aperturing.
D) Hydraulic Needling
Hydraulic needling is one approach to remove, puncture, or
micro-slit one skin of the foam. The pressure in the water jets,
the water columnar diameter, the jet density, the speed at which
the web passes through the jets, the foraminous sheet support
backing, the vacuum dewatering levels, and the number of passes (or
number of banks of jets) determine the level to which the skin
layer is removed. Several thermoplastic foams have been treated in
this manner to enhance properties. In addition to skin layer
removal, an increase in open-cell content and liquid accessible
pore space has been demonstrated.
Several polystyrene-based extruded foams of the invention (Foams
D1-D4 below) made on a pilot line were hydraulically needled at
different pressures (4000-7000 KPa) using a hydraulic needling
tablewasher. Scanning Electron Microscopy of the needled foams show
that the skin layer was punctured, allowing access to the open
cells below. The data in Table D1 (below) shows that hydraulic
needling at the stated pressures improves the absorption capacity,
vertical wicking height, and open-cell content of the foam.
TABLE-US-00001 TABLE D1 Foam D1 Foam D2 Foam D3 Foam D4 4137 5556
5556 6945 4827 5556 5556 6945 Control Kpa Kpa Control Kpa Kpa
Control Kpa Kpa Control Kpa Kpa Basis 249 220 234 313 237 238 227
180 188 252 237 238 weight (g/m{circumflex over ( )}2) Dry Bulk
2.99 2.51 2.31 3.08 1.67 1.65 2.81 1.98 2.27 1.97 1.67 1.65 (mm)
Capacity 0.5 1.9 2.2 0.4 1.1 1.2 0.4 1.6 2.3 0.4 1.1 1.2 (g/g)
Open-cell 60 71 80 74 66 63 55 60 70 55 66 63 (%) Vertical 4.1 7.5
8 3.1 8.2 8.2 3.2 5.1 5.3 4.2 8.2 8.2 wicking (cm)
Polystyrene/KRATON.RTM. blend foams (Foams D5-D7) were made on a
pilot line and hydraulically needled using a hydraulic needling
tablewasher at about 5556 KPa. Results from sample characterization
are shown in Table D2 (below).
TABLE-US-00002 TABLE D2 Foam D5 Foam D6 Foam D7 Control H-needled
Control H-needled Control H-needled Basis weight (g/m{circumflex
over ( )}2) 150 150 150 150 150 150 Dry Bulk (mm) 1.29 1.83 1.5
1.92 3.19 2.59 Capacity (g/g) 0.9 6.3 1.7 7.2 6.2 12.3 Open-cell
(%) 63 89 82 90 90 94 Vertical wicking (cm) 10 16 10 15 4 14
Bending Modulus (MD) (Kpa) 26290 2703 28938 6516 7667 2751 Bending
Modulus (CD) (Kpa) 8743 1469 4675 2558 4054 1089
FIG. 7 illustrates one suitable hydraulic needling process which
can be tailored to perforate only one skin. The hydraulic needling
process may be carried out with any appropriate working fluid such
as, for example, water. The working fluid is generally evenly
distributed by the manifold 692 through a series of individual
holes or orifices 694 which may be from about 0.003 to about 0.015
inch (0.076 to 0.391 mm) in diameter and are used to discharge fine
columnar jets or needles of fluid. In some aspects, the working
fluid passes through the orifices 694 at a pressure generally
ranging from about 500 to about 1000 pounds per square inch gage
(psig) (3447 to 6895 KPa), such as about 600 to about 800 psig
(4137 to 5516 KPa). In general, the integrated foam layers may be
hydraulically needled on one side using one to four manifolds.
Greater energy, including intermittently impulsed needling energy,
may be needed if the hydraulic needling, in addition to perforating
one of the skins, is used to form apertures 62 (FIG. 4), or when
high line speeds are employed.
Water jet treatment equipment and other hydraulic needling
equipment and processes which may be adapted can be found, for
example, in U.S. Pat. No. 3,485,706 to Evans, and in an article by
Honeycomb Systems, Inc. entitled "Rotary Hydraulic Entanglement of
Nonwovens," reprinted from INSIGHT 86 INTERNATIONAL ADVANCED
FORMING/BONDING CONFERENCE, both of which are incorporated herein
by reference in a manner consistent herewith. In some aspects, the
invention may be practiced using a manifold containing an orifice
strip having 0.007 inch (0.18 mm) diameter orifices, 30 orifices
per inch (12 orifices per cm), and one row of orifices such as that
produced by Metso Paper USA, Inc., a business having offices
located in Biddeford, Me., U.S.A. Other manifold configurations and
combinations, such as those available from Fleissner GmbH, a
business having offices in Egelsbach, Germany, or Rieter Perfojet
S.A., a business having offices located in Winterthur, Switzerland,
may also be used. For instance, in some aspects a single manifold
may be utilized, whereas in other aspects several manifolds may be
arranged in succession.
Referring again to FIG. 7, the fine columnar jetted streams 696 of
the working fluid impact on the foam layer 682, thereby puncturing
only one of the skins formed on the foam layer surfaces during
formation and increase the open-cell content of that surface.
Vacuum slots in suction box(es) 695 can be located at the jets and
downstream of the needling manifold(s) 694 to remove excess water
from the hydraulically jet-treated material 698. A foraminous
moving wire 690 is generally used to convey and support the foam
sheet 682. The hydraulically jet-treated integrated hybrid foam
layer 698 can then be dried using means known in the art.
E) Areal Sheet Splitting
Typically, an extruded thermoplastic foam sheet upon being
discharged from an extrusion die has z-directional cell shape and
size gradients that correspond to how close cells are located
proximal to the peripheral skin surfaces. At selected processing
conditions, internal cells generally grow to much larger sizes than
cells located near the outer surfaces of the sheet. This process
can be enhanced where cell walls in the middle of the sheet form a
channel for they are nearly non-existent and the cell struts are
thin and few in number. Such sheets can be separated along the
internal channel where such large open cells form a
demarcation.
The method for producing delaminable foam requires a foam extrusion
process that produces foam sheets with an internal cell structure
that is conducive to delamination or areal splitting. After the
sheet is extruded, it is fed through a sheet delaminating station.
One option is to have a delaminating station having two vacuum
rolls positioned to form a nip opening distance near equal to the
foam sheet thickness. The two rolls move at the same synchronized
circumferential speeds with two sheet take-off angles aligned
downstream of the nip to follow the rolls' radial curvatures to
position the sheet's opposite peripheral surfaces to be near normal
to the initial sheet path direction. This arrangement allows the
sheet to readily split into two separate webs at the sheet's
centerline where internal cells are large and few thin struts
occur. The sheet vacuum hold down force for each roll must be
greater than the sheet travel force to maintain the delaminating or
areal splitting action of the foam. With change in sheet direction
occurring with the two rolls radial curvatures, the resultant
forces cause the sheet to delaminate since both sides of the sheet
remain fixed to the rotating vacuum rolls.
Acceptable foam was made on a pilot line using blends of
polystyrene, Kraton elastomer, surfactant, and talc, a nucleant.
These materials were melted in a first extruder where they were
mixed together and combined with blowing agents. The blowing agents
were isopentane and carbon dioxide. The gas laden melt was
transferred to a second extruder where the melt was cooled before
being extruded through an annular die. The melt expanded into foam
upon discharge. The foam tube was then stretched and cooled over a
mandrel drum and slit into a sheet before being wound into roll
form. A single extruder (typically a twin screw extruder) can be
used in lieu of the aforementioned tandem extrusion system;
however, basic process steps remain essentially the same.
Process conditions are typically optimized for throughput and foam
uniformity. Uniformity of cell structure and isotropy of cell shape
throughout the sheet are enhanced by ensuring proper mixing of
materials and blowing agents and adjusting process conditions that
ensure adequate solubility of the blowing agent(s). The method by
which a foam sheet is cooled will typically affect cell properties
near the peripheral surfaces of a foam sheet. The cells nearest the
peripheral surfaces typically collapse and form a skin or film that
is non-permeable or nearly non-permeable to fluid. The rate a sheet
is pulled from the die opening and across a cooling drum has a
major impact on the sheet and the cells making it up. A typical
foam manufacturer focuses on cooling the material at a slow enough
rate that the blowing agent(s) has (have) time to diffuse through
the polymer melt and to form bubbles or cells of sufficient size
yet the blowing gas diffusivity is slow enough so the foam cells
can gain structural stability. The cooling rate is adjusted by
adjusting the environment that the foam can expand into and by
controlling the temperature of the surfaces onto which the foam
contacts. As the polymer melt cools, gas permeability decreases and
the foam sheet tends to retain the blowing agents longer which
increases foam cell size. Typical foam manufacturers hold value in
having uniform cell size and therefore require careful adjustment
and control of cooling to maintain uniform cell size throughout the
thickness of the sample. It is possible to adjust the foam process
so cellular growth increases in the center of the foam sheet
relative to cells near the peripheral surfaces. In this invention,
a foam sheet is made that is particularly easy to delaminate or
"areal split" along the central internal channel or axis of the
sheet and is due to the large cells and few thin struts. "Areal
split" means foams that require little force to continuously pull
the top surface away from the bottom surface while the two
separated webs remain intact and near uniform without unwanted
tears.
In summary, process conditions used to make areal splittable foam
generally include the following: 1. Upon discharge, the foam
surfaces are cooled quickly to reduce the diffusivity rate of the
blowing agent(s). 2. The foam is pulled out of the die at a rate at
or slightly faster than the velocity of the exiting melt; i.e.,
causing no stretching and/or cellular elongation. 3. An "excess" of
blowing agent(s) is (are) provided to the melt. "Excess" refers to
a concentration greater than the typical minimum concentration used
to produce the targeted density.
As shown in FIG. 14, one delaminating process 700 consists of two
vacuum rolls 702 and 704 that form a nip 706 and rotate in opposite
directions to provide force to pull the top sheet surface 708 away
from the bottom surface 710. The foam is held in place against
these rolls by the pressure drop across the sheet 705 caused by the
vacuum at the surface of the rolls. The vacuum rolls 702 and 704
are designed to prevent substantial deformation of the sheet 705 at
the location where the splitting action takes place. This is
accomplished with a fine mesh foraminous screen cover 707 on the
surface of the rotating vacuum rolls and internal vacuum
distribution baffles to evenly distribute the pressure forces and
by use of a stretching station 712 to tender and level the sheet
705 before it is fixed to the initial vacuum roll 702. To
facilitate the splitting of the sheet, pre-conditioning of the
sheet can be performed. Pulling materials through an "S-wrap" 711
as shown will tend to put shear stresses in the sheet 705. These
shear forces can break many of the internal thin channel struts
that link the top and bottom layers. In addition, rolls 713
positioned immediately upstream of the vacuum rolls can either add
heat, or cool the sheet 705 to facilitate efficient and uniform
splitting. Cooling the sheet can bring the sheet below its rubber
transition facilitating breaking of the struts with less strain.
Alternately, heating the sheet can reduce the stress required to
break struts.
Another delaminating process 800 is shown in FIG. 15 and can be
used to split the top surface 806 from the bottom 808. In this
apparatus, two small splitting rolls 802 and 804 form a nip 810 and
provide surfaces for the sheet 805 to be pulled against. This
design provides a method for increasing the rate that sheets are
pulled apart. Small splitting roll radii create fast splitting
rates. With this device, the distance between the splitting rolls
can be controlled to nip the foam 805 so it has a sheet speed equal
to the circumferential speeds of the two synchronized rotating
rolls 802 and 804. A driven pull roll system including nips 814 and
816 and S-roll nips 818 and 820 can be used to put tension in the
sheet that is sufficient to split the foam sheet apart. Again, the
foam 805 can be pre-stretched using a stretching station 812
including S-rolls 811 and 813. The delamination process 800 is
useful for foams having low splitting forces because it has fewer
components and no vacuum system.
Calendaring and creping can also be used to soften and rupture cell
membranes to improve cellular connectivity, and thermoforming can
be used to shape the foam absorbent. Mechanical, hydraulic, and
thermal perforation can also be used to soften foam and further
increase open-cell content.
Post-densification of the foam structure, after extrusion, can be
employed to enhance functionality. The integrated hybrid foam layer
can then be laminated to other layers, or used alone, resulting in
structures having various functionalities. Various foregoing
techniques can be employed to make an integrated hybrid foam layer
that is receptive to printing using non-solvent flexographic inks
on the open surface.
A wide variety of foam compositions are useful for preparing the
integrated hybrid foam layer. Exemplary thermoplastic foam
compositions are described in detail in U.S. Patent Application
Publication 2005/0124709 A1, published on 9 Jun. 2005, the
disclosure of which is incorporated by reference. Pertinent details
are provided as follows.
In one embodiment, the foam polymer composition may include one or
more surfactants and a plasticizing agent in combination with a
base resin. The amount of surfactant and/or plasticizing agent can
be adjusted in order to control softness, open-cell content, and
cellular size and structure of the resulting foam. A thermoplastic
elastomer can be added to the foam polymer composition in addition
to, or in place of, the plasticizing agent to enhance the
resiliency, flexibility, softness, and elasticity of the resulting
foam.
The base resin, or starting material, included in the foam
composition can include any suitable thermoplastic polymer, or
blend of thermoplastic polymers, or blend of thermoplastic and
non-thermoplastic polymers.
Examples of polymers, suitable for use as base resins, include
styrene polymers, such as polystyrene or polystyrene copolymers or
other alkenyl aromatic polymers; polyolefins including homo or
copolymers of olefins, such as polyethylene, polypropylene,
polybutylene, etc.; polyesters, such as polyalkylene terephthalate;
and combinations thereof. A commercially available example of
polystyrene resin is Dow STYRON.RTM. 685D, available from Dow
Chemical Company in Midland, Mich., U.S.A.
Coagents and compatibilizers can be utilized for blending the base
resins. Crosslinking agents can also be employed to enhance
mechanical properties, foamability and expansion. Crosslinking may
be done by several means including electron beams or by chemical
crosslinking agents including organic peroxides. Use of polymer
side groups, incorporation of chains within the polymer structure
to prevent polymer crystallization, lowering of the glass
transition temperature, lowering a given polymer's molecular weight
distribution, adjusting melt flow strength and viscous elastic
properties including elongational viscosity of the polymer melt,
block copolymerization, blending polymers, and use of polyolefin
homopolymers and copolymers have all been used to improve foam
flexibility and foamability. Homopolymers can be engineered with
elastic and crystalline areas. Syndiotactic, atactic, and isotactic
polypropylenes, blends of such and other polymers can also be
utilized. Suitable polyolefin resins include low, including linear
low, medium and high-density polyethylene and polypropylene, which
are normally made using Ziegler-Natta or Phillips catalysts and are
relatively linear; generally more foamable are resins having
branched polymer chains. Isotactic propylene homopolymers and
blends are made using metallocene-based catalysts. Olefin
elastomers are included.
Ethylene and .alpha.-olefin copolymers, made using either
Ziegler-Natta or a metallocene catalyst, can produce soft, flexible
foam having extensibility. Polyethylene cross-linked with
.alpha.-olefins and various ethylene ionomer resins can also be
utilized. Use of ethylene-vinyl acetate copolymers with other
polyolefin-type resins can produce soft foam. Common modifiers for
various polymers can also be reacted with chain groups to obtain
suitable functionality. Suitable alkenyl aromatic polymers include
alkenyl aromatic homopolymers and copolymers of alkenyl aromatic
compounds and copolymerizable ethylenically unsaturated comonomers,
including minor proportions of non-alkenyl aromatic polymers and
blends of such. Ionomer resins can also be utilized.
Other polymers that may be employed as base resins and
thermoplastic elastomers include natural and synthetic organic
polymers including cellulosic polymers, methyl cellulose,
polylactic acids, polyvinyl acids, polyacrylates, polycarbonates,
starch-based polymers, polyetherimides, polyamides, polyesters,
polymethylmethacrylates, and copolymer/polymer blends.
Rubber-modified polymers such as styrene elastomers,
styrene/butadiene copolymers, ethylene elastomers, butadiene, and
polybutylene resins, ethylene-propylene rubbers, EPDM, EPM, and
other rubbery homopolymers and copolymers of such can be added to
enhance softness and hand. Olefin elastomers can also be utilized
for such purposes. Rubbers, including natural rubber, SBR,
polybutadiene, ethylene propylene terpolymers, and vulcanized
rubbers, including TPVs, can also be added to improve rubber-like
elasticity.
Thermoplastic foam absorbency can be enhanced by foaming with
spontaneous hydrogels, commonly known as superabsorbents.
Superabsorbents can include alkali metal salts of polyacrylic
acids; polyacrylamides; polyvinyl alcohol; ethylene maleic
anhydride copolymers; polyvinyl ethers; hydroxypropylcellulose;
polyvinyl morpholinone; polymers and copolymers of vinyl sulfonic
acid, polyacrylates, polyacrylamides, polyvinyl pyridine; and the
like. Other suitable polymers include hydrolyzed acrylonitrile
grafted starch, acrylic acid grafted starch,
carboxy-methyl-cellulose, isobutylene maleic anhydride copolymers,
and mixtures thereof. Further suitable polymers include inorganic
polymers, such as polyphosphazene, and the like. Furthermore,
thermoplastic foam biodegradability and absorbency can be enhanced
by foaming with cellulose-based and starch-based components such as
wood and/or vegetable fibrous pulp/flour.
The foam polymer composition may also, or alternatively, include
diblock, triblock, tetrablock, or other multi-block thermoplastic
elastomeric and/or flexible copolymers such as polyolefin-based
thermoplastic elastomers including random block copolymers
including ethylene .alpha.-olefin copolymers; block copolymers
including hydrogenated butadiene-isoprene-butadiene block
copolymers; stereoblock polypropylenes; graft copolymers, including
ethylene-propylene-diene terpolymer or ethylene-propylene-diene
monomer (EPDM), ethylene-propylene random copolymers (EPM),
ethylene propylene rubbers (EPR), ethylene vinyl acetate (EVA), and
ethylene-methyl acrylate (EMA); and styrenic block copolymers
including diblock and triblock copolymers such as
styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS),
styrene-isoprene-butadiene-styrene (SIBS),
styrene-ethylene/butylene-styrene (SEBS), or
styrene-ethylene/propylene-styrene (SEPS), which may be obtained
from Kraton Polymers of Belpre, Ohio, U.S.A., under the trade
designation KRATON.RTM. elastomeric resin or from Dexco, a division
of ExxonMobil Chemical Company in Houston, Tex., U.S.A., under the
trade designation VECTOR.RTM. (SIS and SBS polymers) or SEBS
polymers as the SEPTON.RTM. series of thermoplastic rubbers from
Kuraray America, Inc. in New York, N.Y., U.S.A. The foam polymer
composition may include blends of thermoplastic elastomers with
dynamic vulcanized elastomer-thermoplastic blends; thermoplastic
polyether ester elastomers; ionomeric thermoplastic elastomers;
thermoplastic elastic polyurethanes, including those available from
E.I. Du Pont de Nemours in Wilmington, Del., U.S.A., under the
trade name LYCRA.RTM. polyurethane, and ESTANE.RTM. available from
Noveon, Inc. in Cleveland, Ohio, U.S.A.; thermoplastic elastic
polyamides, including polyether block amides available from ATOFINA
Chemicals, Inc. in Philadelphia, Pa., U.S.A., under the trade name
PEBAX.RTM. polyether block amide. The foam polymer composition may
include thermoplastic elastic polyesters, including those available
from E.I. Du Pont de Nemours Company, under the trade name
HYTREL.RTM., and ARNITEL.RTM. from DSM Engineering Plastics of
Evansville, Ind., U.S.A., and single-site or metallocene-catalyzed
polyolefins having a density of less than about 0.89 grams/cubic
centimeter such as metallocene polyethylene resins, available from
Dow Chemical Company in Midland, Mich., U.S.A. under the trade name
AFFINITY.TM.; polyethylene-based elastomers from ExxonMobil
Chemical Co. of Houston, Tex., U.S.A under the trade name
EXACT.TM.; and combinations thereof.
As used herein, a tri-block copolymer has an ABA structure where
the A represents several repeat units of type A, and B represents
several repeat units of type B. As mentioned above, several
examples of styrenic block copolymers are SBS, SIS, SIBS, SEBS, and
SEPS. In these copolymers the A blocks are polystyrene and the B
blocks are the rubbery component. Generally these triblock
copolymers have molecular weights that can vary from the low
thousands to hundreds of thousands and the styrene content can
range from 5% to 75% based on the weight of the triblock copolymer.
A diblock copolymer is similar to the triblock but is of an AB
structure. Suitable diblocks include styrene-isoprene diblocks,
which have a molecular weight of approximately one-half of the
triblock molecular weight and having the same ratio of A blocks to
B blocks. Diblocks with a different ratio of A to B blocks or a
molecular weight larger or greater than one-half of triblock
copolymers may be suitable for improving the foam polymer formula
for producing low-density, soft, flexible, absorbent foam via
polymer extrusion.
It may be particularly beneficial to include a thermoplastic
elastomer having a high diblock content and high molecular weight
as part of the foam polymer formula to extrude low-density, soft,
flexible, resilient, absorbent, thermoplastic foam. For example,
the thermoplastic elastomer may have a diblock content between
about 50% and about 80%, by weight, of the total thermoplastic
elastomer weight.
KRATON.RTM. products, available from KRATON Polymers LLC, have been
shown to act as a discontinuous phase in styrenic-based foams and
act as cell-opener generators when used in small amounts. The
amount of KRATON.RTM. polymers used in the foam polymer composition
as a whole is of such a large magnitude that the cell-opener effect
is negligible compared to the resiliency, flexibility, elasticity,
and softness imparted.
Suitably, the foam polymer composition includes up to about 90% by
weight of polystyrene, and at least 10% by weight of thermoplastic
elastomer. More particularly, the foam polymer composition may
include between about 45% and about 90% by weight of polystyrene,
and between about 10% and about 55% by weight of thermoplastic
elastomer. Alternatively, the foam polymer composition may include
between about 50% and about 80% by weight of polystyrene, and
between about 20% and about 50% by weight of thermoplastic
elastomer. In one embodiment, for example, the foam polymer
composition may include equal amounts of polystyrene and
thermoplastic elastomer.
In another embodiment, the foam polymer composition may include
about 40% to about 80% by weight polystyrene and about 20% to about
60% by weight thermoplastic elastomer. In another embodiment, the
foam polymer composition may include about 50% to about 70% by
weight polystyrene and about 30% to about 50% by weight
thermoplastic elastomer.
A plasticizing agent can be included in the foam polymer
composition. A plasticizing agent is a chemical agent that imparts
flexibility, stretchability and workability. The type of
plasticizing agent has an influence on foam gel properties, blowing
agent migration resistance, cellular structure, including the fine
cell size, and number of open cells. Typically plasticizing agents
are of low molecular weight. The increase in polymer chain mobility
and free volume caused by incorporation of a plasticizing agent
typically results in a Tg decrease, and plasticizing agent
effectiveness is often characterized by this measurement.
Petroleum-based oils, fatty acids, and esters are commonly used and
act as external plasticizing agents or solvents because they do not
chemically bond to the polymer yet remain intact in the polymer
matrix upon crystallization.
The plasticizing agent increases cell connectivity by thinning
membranes between cells to the point of creating porous connections
between cells; thus, the plasticizing agent increases open-cell
content. Suitably, the plasticizing agent is included in an amount
between about 0.5% and about 10%, or between about 1% and about
10%, by weight, of the foam polymer composition. The plasticizing
agent is gradually and carefully metered in increasing
concentration into the foam polymer formula during the foaming
process because too much plasticizing agent added at once creates
cellular instability, resulting in cellular collapse.
Examples of suitable plasticizing agents include polyethylene,
ethylene vinyl acetate, mineral oil, palm oil, waxes, esters based
on alcohols and organic acids, naphthalene oil, paraffin oil, and
combinations thereof. A commercially available example of a
suitable plasticizing agent is a small-chain polyethylene that is
produced as a catalytic polymerization of ethylene; because of its
low molecular weight it is often referred to as a "wax." This
low-density, highly branched polyethylene "wax" is available from
Eastman Chemical Company of Kingsport, Tenn., U.S.A., under the
trade designation EPOLENE.RTM. C-10.
In order for the foam to be used in personal care and medical
absorbent applications and many absorbent wiping articles and
non-personal care articles, the foam must meet stringent chemical
and safety guidelines. A number of plasticizing agents are
FDA-approved. These plasticizing agents include: acetyl tributyl
citrate; acetyl triethyl citrate; p-tert-butylphenyl salicylate;
butyl stearate; butylphthalyl butyl glycolate; dibutyl sebacate;
di-(2-ethylhexyl) phthalate; diethyl phthalate; diisobutyl adipate;
diisooctyl phthalate; diphenyl-2-ethylhexyl phosphate; epoxidized
soybean oil; ethylphthalyl ethyl glycolate; glycerol monooleate;
monoisopropyl citrate; mono-, di-, and tristearyl citrate;
triacetin (glycerol triacetate); triethyl citrate; and
3-(2-xenoyl)-1,2-epoxypropane.
In certain embodiments, the same material used as the thermoplastic
elastomer may also be used as the plasticizing agent. For example,
the KRATON.RTM. polymers, described above, may be used as a
thermoplastic elastomer and/or a plasticizing agent. In this case,
the foam polymer formula may include between about 10% and about
50% by weight of a single composition that acts as both a
thermoplastic elastomer and a plasticizing agent. Described in an
alternative manner, the foam may be formed without a plasticizing
agent per se; in which case, the foam polymer formula may include
between about 10% and about 50% by weight of the thermoplastic
elastomer.
Foaming of soft, flexible polymers, such as thermoplastic
elastomers, to a low density is difficult to achieve. The addition
of a plasticizing agent makes foaming to low densities even more
difficult to achieve. The use of a surfactant in the foam polymer
composition helps to overcome this difficulty. The surfactant
stabilizes the cells, thereby counteracting cellular collapse while
retaining an open-cell structure. This stabilization of the cells
creates cell uniformity and control of cell structure. In addition
to enabling foaming of plasticized thermoplastic elastomer polymer
containing foam formulations to low densities, the surfactant also
provides wettability to enable the resulting foam to absorb
fluid.
While it is not intended to limit the invention to a particular
theory, it is believed that improved cell stabilization is achieved
via the use of surfactant in a foam polymer formula containing a
plasticizing agent. The addition of a plasticizing agent makes
foaming to low densities even more difficult to achieve.
Plasticizing agents such as waxes, oils, silicone defoamers, and
small particulates at low addition provide localized surface
tension reduction in the foam cell membrane, which causes rupturing
and premature cellular collapse or coalescence. The addition of a
surfactant in the foam polymer composition counteracts
thermodynamic and kinetic instabilities of bubble formation in the
polymer melt. The surfactant stabilizes the cells, thereby
counteracting cellular collapse caused by the plasticizing agent.
This stabilization of the cells creates cell uniformity in terms of
cell size and cell size distribution and thereby allows control of
cell structure. Since the surfactant is a surface active agent, it
lowers the surface or interfacial tension and thus assists bubble
formation. A decreased surface tension reduces the pressure
differential required to maintain a bubble of a certain size,
reduces the pressure difference between bubbles of different sizes,
reduces the free energy required to maintain a given interfacial
area, and thus increases the bubble nucleation rate. As Gibbs
theorem explains, a surfactant combats excessive thinning of cell
membranes and restores surfactant concentration to the surface and
thereby acts as a stabilizing factor; however, a surfactant does
not restore liquid to the film, which results in a lack of
self-repair. The Marangoni effect describes surface flow of
dragging underlying layers of liquid to restore film thickness,
which enhances film elasticity and resilience and thus counters
cellular coalescence. This again is a stabilizer. Assuming the
credence of these two mechanisms, a surfactant would be most
effective if it is designed so that the Marangoni effect dominates
the foam polymer formula, for if the Gibbs effect dominates, the
diffusion rate would be too high and self-repair would not occur.
Therefore the addition of surfactant acts as a "buffer" or
"stabilizer" to control surface tension and with control of
temperature, which also affects surface tension, melt viscosity and
melt strength, bubble stability can occur so that cells form in the
thermoplastic melt. This effect is offset by lowering the surface
tension forces that hold the polymer matrix together.
Bubble walls typically drain due to gravity and capillary forces.
Such drainage thins the walls before the cell struts are
sufficiently hardened, which leads to cell collapse. La Place and
Young proposed that capillary pressure at the junction of two or
more ribs is lower, thereby creating flow from the membrane to the
ribs and, consequently, thinning. With a sufficient amount of
surfactant molecules arranged preferentially to migrate to the
surface of the film membrane, the presence of surfactant at the
membrane's thin film surfaces provides resistance to drainage of
the molten plastic. If the film layer is sufficiently thick, such
as in a foam membrane, it can be further stabilized by an ionic
double layer of molecules resulting from orientation of ionic
surfactants. Both nonionic and ionic surfactants can exhibit
another stabilizing force if the membrane is sufficiently thin.
This would be done by the alignment of surfactant tails to create a
bi-layer structure, such as found in biological cells, that is held
together via Van der Waals forces and thus stabilizes the foam
membrane.
(References: Polymeric Foams, edited by Daniel Klempner and Kurt
Frisch, Hanser Publishers, 1991; and Foam Extrusion, edited by S.
T. Lee, Technomic Publishing Co., Inc., 2000.)
The surfactant is thought to also provide resistance to diffusion
of the gas from the cell to the surroundings, which also aids in
resisting collapse. The reduced gas permeability due to the
drainage resistance is related to the degree the surfactant can
pack into the bubble's film surface and explains the difference
between the performances of the various surfactants. This reduced
rate of diffusion allows sufficient cooling for strut formation to
prevent coalescence. This reduced rate of diffusion allows
sufficient cooling for strut formation to prevent coalescence. The
surfactant does not need to prevent drainage, but simply slows it
sufficiently so that the cell struts are substantially hardened
thereby preventing cell coalescence. In general terms, it is
expected that surfactants that are highly mobile in the melt,
highly surface active, and can pack tightly and prevent membrane
drainage will provide the best cell stabilization.
The surfactant may be a single surfactant, or a multi-component
surfactant system. A multi-component surfactant system is a
combination of two or more surfactants. It has been found that
certain multi-component surfactant systems can achieve equal or
better foam formation at a lower dosage than certain
single-component surfactant systems.
The polymer melt can be continuously extruded to form a soft,
flexible, open-cell, thermoplastic, absorbent foam. As explained
above, the open-cell content of the foam is controlled by adjusting
the amounts of plasticizing agent and surfactant. Open-cell content
can be measured using a gas pycnometer according to ASTM D2856,
Method C. The open-cell content of the resulting foam is suitably
about 50% or greater, or about 70% or greater, or about 80% or
greater.
The surfactant can be included in the foam polymer composition in
an amount between about 0.05% and about 10%, or between about 0.1%
and about 5%, by weight. In an embodiment in which the surfactant
is a multi-component surfactant system, the total of all
surfactants can be included in the foam polymer composition in an
amount between about 0.05% and about 8.0%, or between about 0.1%
and about 3.0%, by weight. Examples of suitable surfactants include
cationic, anionic, amphoteric, and nonionic surfactants. Anionic
surfactants include the alkylsulfonates. Examples of commercially
available surfactants include HOSTASTAT.RTM. HS-1, available from
Clariant Corporation in Winchester, Va., U.S.A.; Cognis
EMEREST.RTM. 2650, Cognis EMEREST.RTM. 2648, and Cognis
EMEREST.RTM. 3712, each available from Cognis Corporation in
Cincinnati, Ohio, U.S.A.; and Dow Corning 193, available from Dow
Chemical Company in Midland, Mich., U.S.A. Alkyl sulfonates are
quite effective; however, use of this class of surfactants in
certain applications may be limited because of product safety. Some
combinations offer unexpected benefits where the alkyl sulfonate is
added at a substantially lower level in conjunction with another
surfactant to yield good foaming and wettability. In one
embodiment, for example, the surfactant can be added to the foam
polymer composition in a gaseous phase, such as through the use of
a blowing agent such as supercritical carbon dioxide. One benefit
of using a gaseous surfactant is that the surfactant can fully
penetrate and be incorporated into the polymer matrix, which can
improve substantivity and thereby reduce surfactant fugitivity to
enhance the foam's permanent wettability.
The balance between cell stabilization of the surfactant and the
enhanced melt drainage from the plasticizing agent enables control
over the open-cell content of the resulting foam. More
particularly, the amount of surfactant can be adjusted to
counteract the effects of the plasticizing agent, and/or the amount
of the plasticizing agent can be adjusted to counteract the effects
of the surfactant. For example, if the plasticizing agent is
included in the foam polymer composition in an amount between about
0.5% and about 5% by weight, then the surfactant should be included
in the foam polymer composition in an amount between about 0.5% and
about 5% by weight. Similarly, if the plasticizing agent is
included in the foam polymer composition in an amount between about
5% and about 10% by weight, then the surfactant should be included
in the foam polymer composition in an amount between about 2% and
about 10% by weight. In addition, the polymer resin melt flow index
can be adjusted to offset the plasticizing agent's effect.
Other additives can be included in the foam polymer composition to
enhance the properties of the resulting foam. As described above, a
nucleant can be added to improve foam gas bubble formation in the
foam polymer composition. Examples of suitable nucleants include
talc, magnesium carbonate, nanoclay, silica, calcium carbonate,
modified nucleant complexes, and combinations thereof. An example
of a commercially available nucleant is a nanoclay available under
the trade name CLOISITE.RTM. 20A, from Southern Clay Products, Inc.
in Gonzales, Tex., U.S.A. The nucleant can be added to the foam
polymer composition in an amount between about 0.1% and about 5% by
weight. Nucleants, or nucleating agents, are described in greater
detail below.
A blowing agent, described in greater detail above, can be added to
the foam polymer composition to aid in the foaming process. Blowing
agents can be compounds that decompose at extrusion temperatures to
release large volumes of gas, volatile liquids such as refrigerants
and hydrocarbons, or ambient gases such as nitrogen and carbon
dioxide, or water, or combinations thereof. A blowing agent can be
added to the foam polymer composition in an amount between about 1%
and about 10% by weight.
Once the foam polymer formula is mixed and formed, including the
plasticizing agent, the surfactant, and any other additives, the
foam polymer composition is heated and mixed, suitably to a
temperature between about 100 and about 500 degrees Celsius, to
create a polymer melt. The plasticizing agent reduces elongational
viscosity of the polymer melt, which leads to foaming difficulties.
However, the surfactant mediates the impact of the plasticizing
agent on the viscosity, thereby providing control over the
open-cell content of the resulting foam. Also, as mentioned, the
polymer resin melt index can be adjusted to offset the plasticizing
agent's effect.
The polymer melt can be foamed using any suitable foaming technique
known to those skilled in the art. The density of the open-celled
foam is suitably about 0.35 g/cm.sup.3 or less, or about 0.20
g/cm.sup.3 or less, or about 0.10 g/cm.sup.3 or less, for example,
about 0.02 to about 0.10 g/cm.sup.3. Foam expansion ratio is
generally about 10 or greater. Suitably, the absorbent foam has
about 5% or more closed cells, or about 10% or more closed cells,
or about 15% or more closed cells to improve resiliency and/or
compression resistance.
The hybrid absorbent foam, and its integrated hybrid foam layer,
can also be characterized in terms of various additional
properties. As explained above, the open-cell content of the foam,
which can be controlled by adjusting the amount of surfactant
and/or plasticizing agent included in the foam polymer formula, is
suitably about 50% or greater, or about 60% greater, or about 70%
or greater, or about 80% or greater, as measured using ASTM D2856.
The foam may also include about 5% or more, or about 10% or more,
or about 15% or more closed cells to improve resiliency and/or
compression resistance. The foam is low density, with a density of
about 0.10 gram/cubic centimeter (g/cm.sup.3) or less, or about
0.07 g/cm.sup.3 or less, or about 0.04 g/cm.sup.3 or less and
suitably at least about 0.02 g/cm.sup.3 (before any compression is
applied to meet specific packaging and/or in-use requirements), is
soft and flexible, and is resilient and elastic with an edge
compression of about 250 grams or less, or about 100 grams or less,
or about 35 grams or less. The foam density is a measurement of
bulk density, determined using ASTM D1622. Edge compression can be
measured using the Edge Compression Test Method, which is described
in detail below. Softness, flexibility, elasticity, and resiliency
are also demonstrated through compression set resistance. The foam
of the invention suitably has a compression resistance of about 20%
compression set or less, or about 15% compression set or less, or
about 7% compression set or less, as measured using ASTM D3575.
The hybrid absorbent thermoplastic foam is soft and flexible. The
hybrid absorbent foam and the integrated hybrid foam layer have a
bending modulus of less than 6000 KPa at 1 mm deflection, suitably
less than 4000 KPa, or less than 2000 KPa, using the Bending
Modulus Test described herein.
Due to surface texturing (described above), the integrated hybrid
foam layer may, on its open surface, have a surface roughness of
about 40 to about 350 microns, suitably about 40 to about 80
microns for lightly textured samples and about 300 to about 350
microns for heavily textured samples, measured using noncontact
optical profilometry as described below. These represent ranges to
produce excellent tactile aesthetics of soft absorbent
thermoplastic foams.
The integrated hybrid foam layer remains suitably absorbent even
after repeated washings. The surfactant permanence remains intact
in the foam such that about 15% or less, or about 10% or less, or
about 5% or less of the surfactant is washed off after soaking in
water for 24 hours. The Surfactant Permanence Test is described in
detail below. An alternative measure of the surfactant permanence
is the surface tension of the supernatant in the same Surfactant
Permanence Test. More particularly, the surface tension of the
supernatant remains greater than about 40 dynes/centimeter, or
greater than about 50 dynes/centimeter, or greater than about 60
dynes/centimeter.
The integrated hybrid foam layer with 0.9% NaCl saline solution has
a saturated capacity of about 1 gram/gram (g/g) or greater, or
about 15 g/g or greater, or about 30 g/g or greater, as measured
under a 0.5 psi (3.45 KPa) load using the Saturated Capacity Test
Method, described in detail below, and a fluid intake flux of about
1 ml/sec/in.sup.2 (0.15 ml/sec/cm.sup.2) or greater, or about 3
ml/sec/in.sup.2 (0.46 ml/sec/cm.sup.2) or greater, or about 5
ml/sec/in.sup.2 (0.77 ml/sec/cm.sup.2) or greater upon the first
insult, about 1 ml/sec/in.sup.2 (0.15 ml/sec/cm.sup.2) or greater,
or about 3 ml/sec/in.sup.2 (0.46 ml/sec/cm.sup.2) or greater, or
about 5 ml/sec/in.sup.2 (0.77 ml/sec/cm.sup.2) or greater upon the
second insult, and about 1 ml/sec/in.sup.2 (0.15 ml/sec/cm.sup.2)
or greater, or about 3 ml/sec/in (0.46 ml/sec/cm.sup.2) or greater,
or about 5 ml/sec/in.sup.2 (0.77 ml/sec/cm.sup.2) or greater upon
the third insult, using the Fluid Intake Flux Test or Modified
Fluid Intatke Flux Test, also described in detail below.
Furthermore, the foam has a vertical wicking height of about 5
centimeters (cm) or higher, or about 7 cm or higher, or about 10 cm
or higher, or about 15 cm or higher in 30 minutes, as measured with
0.9% NaCl saline solution using the Vertical Wicking Test, also
described in detail below.
The integrated hybrid foam layer may have a vertical wicking fluid
flux at zero height of at least about 5 g/sec/m.sup.2, or at least
about 7 g/sec/m.sup.2, or at least about 10 g/sec/m.sup.2, measured
using the Vertical Wicking Fluid Flux Test described herein. The
foam may have a functional capacity greater than about 0.1 gram/cc,
suitably greater than about 0.4 gram/cc, or about 0.1 to about 1.0
gram/cc, measured using the Functional Capacity Test described
herein.
The integrated hybrid foam layer may be thin, but possesses
considerable strength. More particularly, the foam layer may have a
basis weight of about 400 grams per square meter or less, with an
overall bulk, measured at 0.05 psi (0.345 KPa) loading, of about 6
millimeters or less. Suitably, the foam layer has a cross-direction
(CD) trap tear strength of about 300 grams or greater, or about 600
grams or greater, or about 1200 grams or greater, and a
machine-direction (MD) trap tear strength of about 300 grams or
greater, or about 600 grams or greater, or about 1200 grams or
greater. Overall bulk can be measured using the Foam Caliper Test
described herein. Trap tear MD/CD strength of the foam may be
measured using ASTM D1117-14.
The integrated hybrid foam layer may have a bending modulus of less
than about 6000 KPa, suitably less than about 4000 KPa, or about
200 to about 2000 KPa, at 1 mm deflection, measured using the
Bending Modulus Test described herein. The foam layer may have a
dry tensile strength of about 5 kg to about 15 kg, suitably about 8
kg to about 12 kg, or about 9 kg to about 10 kg, measured using the
Dry Tensile Strength Test described herein. The foam layer may have
a wet tensile strength of about 5 kg to about 15 kg, suitably about
7 kg to about 12 kg, or about 8.5 kg to about 10 kg, measured using
the Wet Tensile Strength Test described herein. The foam layer may
have a Wet Tensile Loss of less than about 10%, suitably less than
about 8%, measured by comparing dry and wet tensile strengths, as
described herein. The foam layer may have a static coefficient of
friction of about 0.20 to about 1.50, typically about 0.40 to about
1.0, measured using the Coefficient Of Friction Test described
herein.
The hybrid absorbent foam of the invention is particularly suitable
for use in a variety of absorbent article applications including,
without limitation, personal care absorbent articles, medical
absorbent articles, and industrial absorbent articles, including
without limitation, absorbent wiping articles. Personal care
absorbent articles include, but are not limited to, absorbent
articles such as disposable diapers, baby wipes, training pants,
child-care pants, swimwear, mitts, and other disposable garments;
feminine-care products including, but not limited to, sanitary
napkins, wipes, menstrual pads, panty liners, panty shields,
interlabials, tampons, and tampon applicators; adult-care products
including, but not limited to, wipes, pads, containers,
incontinence products, and urinary shields. Medical absorbent
articles include professional and consumer health medical care
products such as products for applying hot or cold therapy,
hospital gowns, surgical drapes, mitts, gloves, bandages, wound
dressings, wipes, covers, containers, filters, disposable garments
and bed pads, medical absorbent garments, underpads, and the like.
Absorbent wiping articles include facial tissue, washcloths, mitts,
cleaning articles including sponges and wipes and impregnated
wipes, towels such as kitchen towels, disposable cutting sheets,
away-from-home towels, wet-wipes, bath tissue, and the like.
Besides use of the hybrid absorbent foam for personal care
absorbent articles, the foam can also be used in a variety of
clothing components, and non-personal care absorbent products
including filters, masks, packaging absorbents, trash bags, stain
removers, applicator mitts for topical compositions, laundry
soil/ink absorbers, detergent agglomerators, lipophilic fluid
separators, cleaning devices, athletic and recreation products, and
construction and packaging uses. Because the hybrid absorbent foam
is thermoplastic, the foam is also recyclable. The hybrid absorbent
foam can be made biodegradable by including biodegradable
thermoplastic polymers in the foam composition such as polylactic
acid, starches, or the like.
Test Methods
Bending Modulus Test
This test is similar to that described in ASTM D 5934. Samples are
cut to have dimensions of 64 mm long.times.38 mm wide (W). The
thickness of the sample (T) is then measured in millimeters. With
reference to FIGS. 8A and 8B, assemble the apparatus 460 so that
the balance 462 is completely on the leveled baseboard 464, and the
loading nose 466 is centered over the weigh pan 468. The fixture
base 470 should be inspected to be sure that the distance between
the centers 472, 474 of the two 1-inch (2.54 cm) diameter cylinders
476, 478 (S) is 40 mm. The fixture base 470 should be placed on the
weigh pan 468 so that the two cylinders 476, 478 are parallel with
the cylinder on the loading nose 466. The caliper 482 should be
adjusted to lower the assembly 480 with the loading nose 466 in
order to be sure that the loading nose 466 is parallel to the
bottom cylinders 476, 478. The sample (not shown) should then be
laid across the bottom cylinders 476, 478 with the longer dimension
along the span. The loading nose 466 should not touch the sample.
At this point, the balance 462 should be tared.
Dial the caliper 482 to move assembly 480 down so that the loading
nose 466 just touches the sample and the balance 462 reading (load)
is 0.5 g. Then zero the caliper 482; this will be the reference
point for deflection measurements. Set a timer (not shown) for 2
minutes. Dial the caliper 482 to move the loading nose 466 down to
1.0 mm distance (D) then start the timer. Record the load (F) in
grams after 2 minutes, then discard the sample. The Bending Modulus
(BM) at 1.0 mm deflection can be calculated in g/mm.sup.2 using the
following formula:
.function..times..times..function..times..times. ##EQU00001##
To convert the BM to KPa, multiply the above result by 9.8.
Static Coefficient of Friction Test
Coefficient of friction was tested in accordance with ASTM D1894
using a Sintech 2/S test apparatus from MTS. The apparatus is set
up as in FIG. 1 method C in ASTM D1894. Sample size is 2.5.times.7
inches (6.35.times.17.8 cm) and wrapped around the sled so that the
tested side is facing out and in contact with the test surface.
Glass was used as the test surface. The static coefficient of
friction was calculated and an average of five samples was
reported.
Dry and Wet Tensile Strength, Wet Tensile Loss
Dry and Wet tensile strength testing was conducted using the cut
strip test method at constant rate of extension in accordance with
ASTM D5035. The sample size was modified from the ASTM method and
was equal to 3.times.6 inches (7.62.times.15.2 cm). The wet
strength was carried out as specified in the ASTM method. No
surfactant was added to the water during the testing. Percent wet
tensile loss is the percent of tensile loss due to wetting the
material. Percent wet tensile loss is calculated with the following
formula: % Wet Tensile Loss=(Dry Tensile-Wet Tensile)/Dry
Tensile*100.
Foam Caliper (Bulk) Test Method
The caliper or thickness of a material, in millimeters, is measured
at 0.05 PSI (0.345 KPa) using a Frazier spring model compressometer
#326 bulk tester with a 2 inch (50.8 mm) foot (Frazier Precision
Instrument Corporation, 925 Sweeney Drive, Hagerstown, Md.,
U.S.A.). Each type of sample is subjected to three repetitions of
testing and the results are averaged to produce a single value.
Saturated Capacity Test Method
Saturated Capacity is determined using a Saturated Capacity (SAT
CAP) tester with a Magnahelic vacuum gage and a latex dam,
comparable to the following description. Referring to FIGS. 9-11, a
Saturated Capacity tester vacuum apparatus 110 comprises a vacuum
chamber 112 supported on four leg members 114. The vacuum chamber
112 includes a front wall member 116, a rear wall member 118 and
two side walls 120 and 121. The wall members are sufficiently thick
to withstand the anticipated vacuum pressures, and are constructed
and arranged to provide a chamber having outside dimensions
measuring 23.5 inches (59.7 cm) in length, 14 inches (35.6 cm) in
width and 8 inches (20.3 cm) in depth.
A vacuum pump (not shown) operably connects with the vacuum chamber
112 through an appropriate vacuum line conduit and a vacuum valve
124. In addition, a suitable air bleed line connects into the
vacuum chamber 112 through an air bleed valve 126. A hanger
assembly 128 is suitably mounted on the rear wall 118 and is
configured with S-curved ends to provide a convenient resting place
for supporting a latex dam sheet 130 in a convenient position away
from the top of the vacuum apparatus 110. A suitable hanger
assembly can be constructed from 0.25 inch (0.64 cm) diameter
stainless steel rod. The latex dam sheet 130 is looped around a
dowel member 132 to facilitate grasping and to allow a convenient
movement and positioning of the latex dam sheet 130. In the
illustrated position, the dowel member 132 is shown supported in a
hanger assembly 128 to position the latex dam sheet 130 in an open
position away from the top of the vacuum chamber 112.
A bottom edge of the latex dam sheet 130 is clamped against a rear
edge support member 134 with suitable securing means, such as
toggle clamps 140. The toggle clamps 140 are mounted on the rear
wall member 118 with suitable spacers 141 which provide an
appropriate orientation and alignment of the toggle clamps 140 for
the desired operation. Three support shafts 142 are 0.75 inches
(1.90 cm) in diameter and are removably mounted within the vacuum
chamber 112 by means of support brackets 144. The support brackets
144 are generally equally spaced along the front wall member 116
and the rear wall member 118 and arranged in cooperating pairs. In
addition, the support brackets 144 are constructed and arranged to
suitably position the uppermost portions of the support shafts 142
flush with the top of the front, rear and side wall members of the
vacuum chamber 112. Thus, the support shafts 142 are positioned
substantially parallel with one another and are generally aligned
with the side wall members 120 and 121. In addition to the rear
edge support member 134, the vacuum apparatus 110 includes a front
support member 136 and two side support members 138 and 139. Each
side support member measures about 1 inch (2.54 cm) in width and
about 1.25 inches (3.18 cm) in height. The lengths of the support
members are constructed to suitably surround the periphery of the
open top edges of the vacuum chamber 112, and are positioned to
protrude above the top edges of the chamber wall members by a
distance of about 0.5 inch (1.27 cm).
A layer of egg crating type material 146 is positioned on top of
the support shafts 142 and the top edges of the wall members of the
vacuum chamber 112. The egg crate material extends over a generally
rectangular area measuring 23.5 inches (59.7 cm) by 14 inches (35.6
cm), and has a depth measurement of about 0.38 inches (0.97 cm).
The individual cells of the egg crating structure measure about 0.5
inch (1.27 cm) square, and the thin sheet material comprising the
egg crating is composed of a suitable material, such as
polystyrene. For example, the egg crating material can be McMaster
Supply Catalog No. 162 4K 14, translucent diffuser panel material.
A layer of 6 mm (0.25 inch) mesh TEFLON.RTM.-coated screening 148,
available from Eagle Supply and Plastics, Inc., in Appleton, Wis.,
U.S.A., which measures 23.5 inches (59.7 cm) by 14 inches (35.6
cm), is placed on top of the egg crating material 146.
A suitable drain line and a drain valve 150 connect to bottom plate
member 119 of the vacuum chamber 112 to provide a convenient
mechanism for draining liquids from the vacuum chamber 112. The
various wall members and support members of vacuum apparatus 110
may be composed of a suitable noncorroding, moisture-resistant
material, such as polycarbonate plastic. The various assembly
joints may be affixed by solvent welding, and the finished assembly
of the tester is constructed to be watertight. A vacuum gauge 152
operably connects through a conduit into the vacuum chamber 112. A
suitable pressure gauge is a Magnahelic differential gauge capable
of measuring a vacuum of 0-100 inches of water (0-186 mmHg), such
as a No. 2100 gauge available from Dwyer Instrument Incorporated in
Michigan City, Ind., U.S.A.
The dry product or other absorbent structure is weighed and then
placed in excess 0.9% NaCl saline solution and allowed to soak for
twenty minutes. After the twenty minute soak time, the absorbent
structure is placed on the egg crate material and mesh
TEFLON.RTM.-coated screening of the Saturated Capacity tester
vacuum apparatus 110. The latex dam sheet 130 is placed over the
absorbent structure(s) and the entire egg crate grid so that the
latex dam sheet 130 creates a seal when a vacuum is drawn on the
vacuum apparatus 110. A vacuum of 0.5 pounds per square inch (psi)
(3.45 KPa) is held in the Saturated Capacity tester vacuum
apparatus 110 for five minutes. The vacuum creates a pressure on
the absorbent structure(s), causing drainage of some liquid. After
five minutes at 0.5 psi (3.45 KPa) vacuum, the latex dam sheet 130
is rolled back and the absorbent structure(s) are weighed to
generate a wet weight.
The overall capacity of each absorbent structure is determined by
subtracting the dry weight of each absorbent from the wet weight of
that absorbent, determined at this point in the procedure. The 0.5
psi (3.45 KPa) SAT CAP or SAT CAP of the absorbent structure is
determined by the following formula: SAT CAP=(wet weight-dry
weight)/dry weight; wherein the SAT CAP value has units of grams of
fluid/gram absorbent. For both overall capacity and SAT CAP, a
minimum of four specimens of each sample should be tested and the
results averaged. If the absorbent structure has low integrity or
disintegrates during the soak or transfer procedures, the absorbent
structure can be wrapped in a containment material such as paper
toweling, for example SCOTT.RTM. paper towels manufactured by
Kimberly-Clark Corporation, Neenah, Wis., U.S.A. The absorbent
structure can be tested with the overwrap in place and the capacity
of the overwrap can be independently determined and subtracted from
the wet weight of the total wrapped absorbent structure to obtain a
wet absorbent weight.
Single Drop Intake Time Test
Ten drops of test fluid are placed at random locations on a 4-inch
(10.16 cm by 10.16 cm) sample of material, and the intake time is
recorded, using the equipment and test procedure below. An average
of the ten recorded times is reported as the single drop fluid
intake time.
Equipment: 1. Test fluid is deionized water with several drops of
blue food coloring in 100 ml. 2. Syringe pump was programmed to
pump 0.038 ml of fluid. 3. Syringe was connected to tubing that was
attached to a hematocrit glass tube with an orifice that has the
size such that 0.038 ml made one drop. 4. A test stand was set up
to hold the tube vertically above the material 1 cm in height. 5.
Stopwatch accurate to 0.1 seconds.
Steps: 1. Start the syringe pump so that it drops one drop at a
randomly chosen location on the foam. 2. As the drop contacts the
test material, start a stopwatch. 3. Stop the timer when the fluid
has sufficiently penetrated into the foam such that the reflection
of light off the fluid is no longer visible. 4. Record the time. 5.
Repeat 10 times in randomly chosen locations that are not close to
previously tested locations.
Fluid Intake Flux Test
The Fluid Intake Flux (FIF) Test determines the amount of time
required for an absorbent structure, and more particularly a foam
sample thereof, to take in (but not necessarily absorb) a known
amount of test solution (0.9 weight percent solution of sodium
chloride in distilled water at room temperature). A suitable
apparatus for performing the FIF Test is shown in FIGS. 12A and 12B
and is generally indicated at 200. The test apparatus 200 comprises
upper and lower assemblies, generally indicated at 202 and 204
respectively, wherein the lower assembly comprises a generally 7
inch (18 cm) by 7 inch (18 cm) square lower plate 206 constructed
of a transparent material such as PLEXIGLAS.RTM. for supporting the
absorbent foam sample during the test and a generally 4.5 inch
(11.4 cm) by 4.5 inch (11.4 cm) square platform 218 centered on the
lower plate 206.
The upper assembly 202 comprises a generally square upper plate 208
constructed similar to the lower plate 206 and having a central
opening 210 formed therein. A cylinder (fluid delivery tube) 212
having an inner diameter of about one inch (2.54 cm) is secured to
the upper plate 208 at the central opening 210 and extends upward
substantially perpendicular to the upper plate. For flux
determination, the inside dimension of the fluid delivery tube
should maintain a ratio between 1:3 and 1:6 of the sample diameter.
The central opening 210 of the upper plate 208 should have a
diameter at least equal to the inner diameter of the cylinder 212
where the cylinder 212 is mounted on top of the upper plate 208.
However, the diameter of the central opening 210 may instead be
sized large enough to receive the outer diameter of the cylinder
212 within the opening so that the cylinder 212 is secured to the
upper plate 208 within the central opening 210.
Pin elements 214 are located near the outside corners of the lower
plate 206, and corresponding recesses 216 in the upper plate 208
are sized to receive the pin elements 214 to properly align and
position the upper assembly 202 on the lower assembly 204 during
testing. The weight of the upper assembly 202 (e.g., the upper
plate 208 and cylinder 212) is approximately 360 grams to simulate
approximately 0.11 pounds/square inch (psi) (0.758 KPa) pressure on
the absorbent foam sample during the FIF Test.
To run the FIF Test, an absorbent foam sample 207 being three
inches in diameter is weighed and the weight is recorded in grams.
The foam sample 207 is then centered on the platform 218 of the
lower assembly 204. To prevent unwanted foam expansion into the
central opening 210, centered on top of the foam sample 207, is
positioned an approximately 1.5 inch diameter piece of flexible
fiberglass standard 18.times.16 mesh window insect screening 209,
available from Phifer Wire Products, Inc., Tuscaloosa, Ala., U.S.A.
The upper assembly 202 is placed over the foam sample 207 in
opposed relationship with the lower assembly 204, with the pin
elements 214 of the lower plate 206 seated in the recesses 216
formed in the upper plate 208 and the cylinder 212 is generally
centered over the foam sample 207. Prior to running the FIF test,
the aforementioned Saturated Capacity Test is measured on the foam
sample 207. Thirty-three percent (33%) of the saturation capacity
is then calculated; e.g., if the test foam has a saturated capacity
of 12 g of 0.9% NaCl saline test solution/g of test foam and the
three inch diameter foam sample 207 weighs one gram, then 4 grams
of 0.9% NaCl saline test solution (referred to herein as a first
insult) is poured into the top of the cylinder 212 and allowed to
flow down into the absorbent foam sample 207. A stopwatch is
started when the first drop of solution contacts the foam sample
207 and is stopped when the liquid ring between the edge of the
cylinder 212 and the foam sample 207 disappears. The reading on the
stopwatch is recorded to two decimal places and represents the
intake time (in seconds) required for the first insult to be taken
into the absorbent foam sample 207.
A time period of fifteen minutes is allowed to elapse, after which
a second insult equal to the first insult is poured into the top of
the cylinder 212 and again the intake time is measured as described
above. After fifteen minutes, the procedure is repeated for a third
insult. An intake flux (in milliliters/second) for each of the
three insults is determined by dividing the amount of solution
(e.g., four grams) used for each insult by the intake time measured
for the corresponding insult. The intake rate is converted into a
fluid intake flux by dividing by the area of the fluid delivery
tube, i.e., 0.79 in.sup.2 (5.1 cm.sup.2).
At least three samples of each absorbent test foam is subjected to
the FIF Test and the results are averaged to determine the intake
time and intake flux of the absorbent foam.
Modified Fluid Intake Flux (FIF) Test for Smaller Foam Samples
The test is done in a similar same manner as described in the
aforementioned standard Fluid Intake Flux (FIF) test; however, this
test was modified to accommodate smaller samples and yet keep the
same fluid delivery tube to sample size ratio as in the standard
FIF test. The modifications included installing the small sample of
non-swelling foam that is to be tested into a suitable holder and
using a suitable fluid delivery tube. The suitable holder can be an
inverted laboratory glass funnel having a uniform diameter
cylindrical output tube of one inch long that rests on top of an
adjustable lab jack platform positioned for downward gravitational
flow. The foam, of sufficient diameter (between 0.18 inch and 0.36
inch, or between 0.46 cm and 0.91 cm) and one inch (2.54 cm) in
length, is gently positioned into the top of the uniform diameter
glass tube of the inverted funnel that is sufficient in size to
hold the foam without significant compression so that one end faces
vertically up (proximal end) and the other end is facing downward
(distal end). The glass tube holds the foam in a stationary
position and is sufficient in length to hold the foam sample yet
then immediately enlarges to the funnel opening to avoid
discharging flow complications of excess fluid after the fluid
leaves the foam's distal end. A fluid delivery tube is constructed
with a 0.06 inch (0.15 cm) diameter orifice and a throat length
that enlarges to a diameter enabling easy dispensation of fluid
into the tube. The enlargement occurs at an approximately 0.25 inch
(0.64 cm) length upstream of the orifice. The fluid delivery tube
is positioned directly above the proximal end of the foam sample
and the inverted funnel and the foam sample is raised using the lab
jack such that the fluid delivery tube is brought into contact with
the foam. Afterwards, similar to the standard FIF test,
thirty-three percent (33%) of the saturation capacity for the foam
sample is then calculated and this volume of 0.9% NaCl saline
solution is dispensed using a PIPETMAN.RTM. P-200 .mu.l pipette,
available from Gilson, Inc. in Middleton, Wis., U.S.A., or similar
pipette, into the fluid delivery tube which measures 0.06 inches
(0.15 cm) in discharge orifice diameter, as opposed to a 1-inch
(2.54 cm) diameter as described in the standard FIF Test, and the
rate of flow is measured with a stopwatch as earlier described. The
preference is to utilize the earlier described standard FIF test
rather than the Modified FIF test and, if discrepancies exist, the
standard FIF test is relied upon.
Vertical Wicking Test Method
A sample of foam is cut and mounted so that it hangs in a vertical
orientation to gravity with an exposed foam edge in a substantially
horizontal orientation. A sufficiently large reservoir of 0.9% NaCl
saline test solution is raised, using a standard lab jack, so that
the foam's horizontal edge extends approximately two millimeters
beneath the surface of the saline. A timer is started simultaneous
to the penetration of the foam into the saline. After thirty
minutes, the height of the fluid in the foam is measured relative
to the surface of the saline. If desired, the saline can contain a
non-surface active, non-chromatographic dye to aid in identifying
the penetration and wicking of the test fluid within the foam.
Alternatively, the foam may be marked at the surface of the fluid
and the fluid reservoir lowered to remove further contact with the
foam. To compensate for possible foam expansion upon hydration, the
foam may be marked at the fluid surface after the wicking time.
Measurement of the fluid height in the foam using the initial foam
dimensions may be done via appropriate means including x-ray
imaging, optical measurement, or slicing sections of the foam until
0.9% NaCl saline test solution is apparent in the slice.
Open Area Test
The open area test is an image analysis for measuring the open area
of a foam surface. The foam surface is colored with a dark pigment
using a black permanent marker. A magnified image of the surface is
acquired with transmitted light using standard microscopy. The
pigmented surface creates enough image contrast between open and
closed areas that standard image analysis software can quantify the
total surface area and the area of the open portions. This
technique can be employed whether the open surface is due to
microaperturing, microslitting, areal splitting, or any other
technique. If the open surface is caused by areal splitting, then
the open surface area is similar to the open-cell content at the
surface.
If the open surface is caused by microaperturing, microslitting, or
some other post-treatment technique besides areal splitting, then
the post-treatment process conditions are adjusted to ensure that
the apertures or other openings are deep enough to penetrate into
the open-cell portion of the integrated hybrid foam layer without
penetrating the closed surface on the opposing side of the foam.
The depth of penetration required, as well as the depth of a
particular opening in a post-treatment foam, can be determined
using scanning electron microscopy ("SEM") of a cross-section of
the integrated hybrid foam layer, and the following procedure: 1.
Take an SEM of the cross section. 2. Using image analysis, quantify
the center of each cell. 3. Optically determine (by user
determination) which cells are open, and which are closed. 4.
Generate a graph that shows the number % of open cells/total cells
as a function of position (depth). 5. Call the boundary the
location where the open-cell percentage exceeds 50%.
Surface Roughness Test
Noncontact optical profilometry was used to determine the average
surface roughness of both sides of two representative hybrid
absorbent foams of the invention. Data was collected using a FRT
MicroProf.RTM. profilometer.
A 10-mm.times.10-mm area of each sample was analyzed. Comparisons
were made between a) untextured samples, b) lightly textured
samples, and c) heavily textured samples. Data spacing was
10-microns based on 1000 lines.times.1000 points/line sampled over
the 10 mm area. Vertical resolution with the 1 mm z-range optical
sensor is better than 100-nanometers (0.1 .mu.m).
The average surface roughness parameter (sPa) is calculated as the
arithmetic average of the absolute deviations about the least
squares (LSQ) best-fit plane through the data. It is the most
widely used measure of surface roughness. It does not distinguish
peaks from valleys but treats both simply as deviations from the
LSQ plane. sPa is the analog of the universal roughness parameter
Ra derived from a line profile, but applied to an area map.
The formula for calculating the surface roughness is described
below:
The definition of average roughness of a surface (x,y) is:
Sa=1/MN.SIGMA..SIGMA.|.eta.(xi,yj)|
(The summations are across the surface i=1 to M, j=1 to N)
M is the number of points per line and N is the number of lines.
.eta. is the deviation from the LSQ plane.
The definition is referenced in, for example, the "Manchester
Report" "Development of Methods for Characterization of Roughness
in Three Dimensions," p. 219, K. J. Stout, ed., Penton Press 1993.
ISBN 1 8571 8023 2.
Data can be filtered using a waviness or roughness filter
(essentially low and high pass filters) prior to calculation of
roughness. Filters are selected based on what aspect of a surface
is most important to measure (for example a speckle structure in a
paint finish or longer wavelength ripples, etc.). The foam data was
not filtered prior to calculation of roughness since there was no
basis to do so, but a filter can be applied.
There was no filtering done to account for waviness in the samples
because the samples were essentially flat over the 10 mm.times.10
mm area of measurement.
Foam samples with no surface texturing had surface roughness
measurements of 4 .mu.m. Similar surface roughness existed on the
closed surface of hybrid absorbent foams of the invention. Lightly
surface textured samples were between 40-60 .mu.m on the open
surface, and heavily textured samples were >300 .mu.m. Good
texturing is achieved at values between 40-350 .mu.m on the open
surface.
The fact that these materials have been apertured does have an
impact on the surface roughness measurements, tending to increase
the value somewhat. The overall impact is below 5% on the samples
tested. The impact would be higher for foams with larger aperture
diameters. It would be possible to get a greater than 40 .mu.m
roughness for an otherwise smooth foam if it contained a large
number of apertures. Such foam would also possess acceptable
texturing even though it doesn't have physical protrusions like
those created by sanding, raising, or sueding.
Surfactant Permanence Test
The Surfactant Permanence Test is based upon the surface tension
depression effect by surfactant addition to water. The surface
tension is measured by the duNouy ring tensiometer method utilizing
a Kruss Processor Tensiometer--K 12 instrument, available from
Kruss USA in Charlotte, N.C., U.S.A. In general terms, a sample of
foam is soaked in distilled water and the surface tension of the
supernatant is measured. This surface tension is compared to a
calibration curve to determine the amount of surfactant washed from
the foam.
Test preparation includes creating a calibration curve for the
particular surfactant utilized. This curve shows the reduced
surface tension of the solution as surfactant concentration
increases. At concentrations above the critical micelle
concentration (CMC), the surface tension reduction from additional
surfactant is minimal.
A sample of pre-weighed foam is placed in distilled water. The
sample is immersed in the room temperature water for 24 hours,
allowing fugitive surfactant to leach out of the foam and dissolve
into the water. The amount of water used is critical. If the amount
of surfactant leached into the water creates a concentration
greater than the CMC, measurement of surface tension on the
solution will only indicate that the concentration is greater than
the CMC. The amount of distilled water used to wash the foam is 100
times the weight of the foam. After the 24-hour soak, the foam is
removed from the water/surfactant solution (supernatant). The water
in the foam is allowed to drain into the supernatant and gentle
pressure is applied to the foam to aid in the removal of excess
supernatant in the foam. The surface tension of the total
supernatant is then measured. Utilizing the calibration curve, the
surface tension corresponds to a weight fraction of surfactant in
the water. This weight fraction is then multiplied by the total
amount of water to yield the weight of surfactant leached from the
foam. The amount of surfactant removed can be expressed as a
fraction of the total surfactant in the initial foam. For example:
foam is made with 10 parts surfactant for every 90 parts foam. A
100 gram sample is soaked in 10,000 grams of distilled water. The
surface tension measurement of the supernatant indicates that the
surfactant concentration in the supernatant is 0.03%. The amount of
surfactant dissolved from the foam is 3.0 grams. The amount of
surfactant in the initial foam was 10 grams, so 30% of the
surfactant was dissolved and 70% of the surfactant remains in the
foam.
With Clariant HOSTASTAT.RTM. HS-1, the CMC is at a concentration of
0.03%, by weight. At concentrations less than the CMC, the surface
tension is described by: .sigma.=5 ln([s])-18 where .sigma. is the
surface tension and [s] is the weight fraction of the surfactant.
As an example, 2.96 grams of an open-cell polystyrene foam made
with 2.5 parts HOSTASTAT.RTM. HS-1 to 100 parts polystyrene was
immersed in 297.79 grams of distilled water for 24 hours. The
surface tension of the supernatant was measured at 39 dynes/cm
which corresponds to 0.0027 grams of surfactant dissolved into the
water, or 3.7% of the total surfactant; therefore, 96.3% of the
surfactant remained in the foam after a 24 hour wash.
Edge Compression Test Method
The method by which the Edge-wise Compression (EC) value can be
determined is set forth below. A 2-inch by 12-inch (5.1 cm by 30.5
cm) piece of absorbent foam is used. The weight of the sample is
determined. The thickness of the material is measured using a hand
micrometer while avoiding surface compression. The material is
formed into a cylinder having a height of 2 inches (5.1 cm), and
with the two ends having 0-0.125 inch (0-3.18 mm) overlap, the
material is stapled together with three staples. One staple is near
the middle of the width of the product, the other two nearer each
edge of the width of the material. The longest dimension of the
staple is in the circumference of the formed cylinder to minimize
the effect of the staples on the testing.
A tensile tester, such as those commercially available from MTS
Systems Corporation in Eden Prairie, Minn., U.S.A., is configured
with a bottom platform, a platen larger than the circumference of
the sample to be tested and parallel to the bottom platform,
attached to a compression load cell placed in the inverted
position. The specimen is placed on the platform under the platen.
The platen is brought into contact with the specimen and compresses
the sample at a rate of 25 mm./min. The maximum force obtained in
compressing the sample to 50% of its width (1 inch) (2.54 cm) is
recorded.
Bucking of the material is identified as a maximum in the
compression force and is typically observed before the material is
compressed to 50% of its uncompressed length. In a product where
the length of the absorbent is less than 12 inches (30.5 cm), the
EC value of the material can be determined in the following manner.
Based on theoretical models governing buckling stresses, in the
Edge-wise Compression configuration described, the buckling stress
is proportional to E*t.sup.2/(H.sup.2) with the proportionality
constant being a function of H.sup.2/(R*t) where E is the Elastic
modulus, H is the height of the cylinder, R is the radius of the
cylinder, and t is the thickness of the material. Expressing the
stress in terms of force per basis weight, it can be shown that the
parameter that needs to be maintained constant is H.sup.2/R.
Therefore, for a sample that is smaller than 12 inches (30.5 cm),
the largest possible circle should be constructed and its height
(width of the sample being cut out) adjusted such that H.sup.2/R
equals 2.1 inches (5.3 cm). A detailed discussion of edge-wise
compression strength has been given in The Handbook Of Physical And
Mechanical Testing Of Paper And Paperboard, Richard E. Mark editor,
Dekker 1983 (Vol. 1).
Vertical Wicking Fluid Flux
Definition:
The vertical wicking fluid flux is the rate of change of fluid mass
that moves vertically against gravity into an absorbent material
per unit of cross sectional area. In general the fluid flux changes
as a function of distance from the surface of the fluid. While
vertical wicking fluid flux can be defined and measured at various
heights/distances from the fluid surface this testing was done at a
zero height. In this way it is not necessary to measure the
distance the fluid has moved as a function of time. It remains only
to measure the time rate of change of fluid mass being absorbed
into the sample and divide that by the cross sectional area of the
material.
Equipment: Apparatus 300 (FIG. 13) including the following: 1.
Balance 302 accurate to at least 0.01 g and capable of
communication with a computer. Connecting hooks 304 connect the
sample holding fixture 306 to the balance 300. 2. Computer and
software to record mass as a function of time accurate to 0.1
seconds. 3. Translational stage 318 capable of at least 2''
vertical travel. The stage needs to move a platform 319 in the
vertical direction with minimal (<1 mm) motion in the horizontal
plane as the stage 318 moves. A suitable platform is 12.7
cm.times.12.7 cm. One electronic stage is sold by Velmex Inc. of
Bloomfield, N.Y. as the translational stage model
#ZMH2504W1-S2.5-FL-BK with a stepper motor and controller model
VXM-1. 4. Clear acrylic tube 312. Tube is 12.7 cm OD and 5.7 cm ID.
The tube should be 25.4 cm in height. 5. Tube Cover. An acrylic top
that is a cylinder 1.9 cm thick with 6.35 cm outer diameter. A lip
is cut so the cover fits part way into the tube. The lip is 0.64 cm
deep in the thickness direction, and 0.38 cm deep in the radius
direction. In the center of the cover a through hole is cut with a
0.32 cm diameter. See the drawings below. 6. Lab jack 322.
Test Method: 1. Ensure the balance 302 is aligned so that holding
mechanism 306 does not touch the tube 312. 2. Cut test material to
6''.times.1'' (15 cm.times.2.5 cm) strips such that the long axis
is aligned with the desired direction of the fluid flow. 3. Weigh
the sample. Measure the caliper of the sample to the nearest 0.05
mm with a pressure of 0.345 KPa. 4. Place sample 308 into clip in
the sample holding mechanism 306. 5. Place the sample 308, the
holding mechanism 306 and the sample chamber lid 310 onto the
sample chamber tube 312. 6. Fill the beaker 314 with 20 ml of test
fluid 316. Use 1% saline with 1 drop blue food coloring per 250 ml
of fluid. Place the beaker 314 on the translational stage 318,
which is controlled with a stepper motor 320. 7. Place the sample
holding chamber 315 over the beaker 314 taking care not to allow
the sample 318 to contact the fluid 316. If necessary adjust the
sample holder 306 to get the sample 318 to be held vertically
without contact with the beaker wall. 8. Connect the sample holding
assembly 306 to the balance at the connecting hook. 9. Adjust the
translational stage 318 and or lab jack 322 so that the sample 318
is approximately 2 mm above the surface of the fluid 316. Ensure
that there is enough remaining travel in the translational stage
318 to move the beaker 314 and fluid 316 into contact with the
sample 308. 10. Adjust the location of the sample chamber 315 so
that the wire from the sample holder 306 is not in contact with
either the vertical sample chamber lid 310 or the hole in the table
303 connecting to the wire to the balance 302. 11. Tare the balance
302. 12. Set up the computer to record the mass every second for
1800 seconds. 13. Move the translational stage 318 so the bottom
edge of the sample is below the surface of the fluid by 2 mm. This
must be done within 5 seconds. 14. If the sample 308 absorbs enough
fluid 316 that the sample 308 is not in contact with the fluid 316
then the data is not valid. Re-run the sample so that the sample is
submerged 4 mm instead of 2 mm. 15. Measure the maximum distance
fluid has moved vertically, subtracting the distance the material
was submerged into the fluid. 16. Measure the caliper 2 mm above
the bottom edge of the sample 308. The caliper measurement should
be done at 0.05 psi (0.345 KPa).
Data Analysis: 1. Using the data recorded calculate the time rate
of change of fluid mass at 1000 seconds. 2. Using the sample width
(2.54 cm) and the sample caliper calculate the cross sectional
area. 3. Calculate the fluid flux at zero height by dividing the
mass flow rate from step 1 by the cross sectional area calculated
in step 2. Ensure the correct units.
It is recognized that some foams with hydration will swell and grow
and therefore change in physical dimensions with fluid wicking.
Significant changes in the cross-sectional area need to be
accounted for in order to measure an accurate fluid flux. In
addition, any significant change in the length of the foam as fluid
is wicked will alter the location of the zero height position above
the fluid reservoir. For these reasons, changes in the setup and
test procedure may be required to accommodate such swellable foams.
Such changes will be apparent to persons skilled in the art. An
example of such a material is a polyurethane foam produced by Rynel
Ltd., Boothbay, Me., U.S.A. and sold as RYNEL.RTM. 562-B.
The embodiments of the invention disclosed herein are exemplary.
Various modifications and improvements can be made without
departing from the spirit and scope of the invention. The scope of
the invention is indicated by the appended claims, and all changes
that fall within the meaning and range of equivalents are intended
to be embraced therein.
* * * * *
References